diff --git a/CHANGELOG.md b/CHANGELOG.md
index 132a4eba4..f70edd917 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,26 @@
 ## 1.55.0
 
+* **Potentially breaking bug fix:** Sass numbers are now universally stored as
+  64-bit floating-point numbers, rather than sometimes being stored as integers.
+  This will generally make arithmetic with very large numbers more reliable and
+  more consistent across platforms, but it does mean that numbers between nine
+  quadrillion and nine quintillion will no longer be represented with full
+  accuracy when compiling Sass on the Dart VM.
+
+* **Potentially breaking bug fix:** Sass equality is now properly [transitive].
+  Two numbers are now considered equal (after doing unit conversions) if they
+  round to the same `1e-11`th. Previously, numbers were considered equal if they
+  were within `1e-11` of one another, which led to some circumstances where `$a
+  == $b` and `$b == $c` but `$a != $b`.
+
+[transitive]: https://en.wikipedia.org/wiki/Transitive_property
+
+* **Potentially breaking bug fix:** Various functions in `sass:math` no longer
+  treat floating-point numbers that are very close (but not identical) to
+  integers as integers. Instead, these functions now follow the floating-point
+  specification exactly. For example, `math.pow(0.000000000001, -1)` now returns
+  `1000000000000` instead of `Infinity`.
+
 * Emit a deprecation warning for `$a -$b` and `$a +$b`, since these look like
   they could be unary operations but they're actually parsed as binary
   operations. Either explicitly write `$a - $b` or `$a (-$b)`. See
@@ -10,6 +31,10 @@
 * Add an optional `argumentName` parameter to `SassScriptException()` to make it
   easier to throw exceptions associated with particular argument names.
 
+* Most APIs that previously returned `num` now return `double`. All APIs
+  continue to _accept_ `num`, although in Dart 2.0.0 these APIs will be changed
+  to accept only `double`.
+
 ### JS API
 
 * Fix a bug in which certain warning spans would not have their properties
diff --git a/lib/src/ast/sass/expression/number.dart b/lib/src/ast/sass/expression/number.dart
index 3467a4af7..ad1f1ed1e 100644
--- a/lib/src/ast/sass/expression/number.dart
+++ b/lib/src/ast/sass/expression/number.dart
@@ -6,6 +6,7 @@ import 'package:meta/meta.dart';
 import 'package:source_span/source_span.dart';
 
 import '../../../visitor/interface/expression.dart';
+import '../../../value/number.dart';
 import '../expression.dart';
 
 /// A number literal.
@@ -14,7 +15,7 @@ import '../expression.dart';
 @sealed
 class NumberExpression implements Expression {
   /// The numeric value.
-  final num value;
+  final double value;
 
   /// The number's unit, or `null`.
   final String? unit;
@@ -26,5 +27,5 @@ class NumberExpression implements Expression {
   T accept<T>(ExpressionVisitor<T> visitor) =>
       visitor.visitNumberExpression(this);
 
-  String toString() => "$value${unit ?? ''}";
+  String toString() => SassNumber(value, unit).toString();
 }
diff --git a/lib/src/exception.dart b/lib/src/exception.dart
index 05f6941a9..0c4c20701 100644
--- a/lib/src/exception.dart
+++ b/lib/src/exception.dart
@@ -171,7 +171,7 @@ class SassScriptException {
   /// triggered this exception. If it's not null, it's automatically included in
   /// [message].
   SassScriptException(String message, [String? argumentName])
-    : message = argumentName == null ? message : "\$$argumentName: $message";
+      : message = argumentName == null ? message : "\$$argumentName: $message";
 
   String toString() => "$message\n\nBUG: This should include a source span!";
 }
diff --git a/lib/src/functions/color.dart b/lib/src/functions/color.dart
index 64e7d35c3..6f0c03a5c 100644
--- a/lib/src/functions/color.dart
+++ b/lib/src/functions/color.dart
@@ -10,8 +10,8 @@ import '../callable.dart';
 import '../evaluation_context.dart';
 import '../exception.dart';
 import '../module/built_in.dart';
-import '../util/number.dart';
 import '../util/nullable.dart';
+import '../util/number.dart';
 import '../utils.dart';
 import '../value.dart';
 
@@ -452,7 +452,7 @@ SassColor _updateComponents(List<Value> arguments,
   ///
   /// [max] should be 255 for RGB channels, 1 for the alpha channel, and 100
   /// for saturation, lightness, whiteness, and blackness.
-  num? getParam(String name, num max,
+  double? getParam(String name, num max,
       {bool checkPercent = false, bool assertPercent = false}) {
     var number = keywords.remove(name)?.assertNumber(name);
     if (number == null) return null;
@@ -500,15 +500,15 @@ SassColor _updateComponents(List<Value> arguments,
   }
 
   /// Updates [current] based on [param], clamped within [max].
-  num updateValue(num current, num? param, num max) {
+  double updateValue(double current, double? param, num max) {
     if (param == null) return current;
     if (change) return param;
-    if (adjust) return (current + param).clamp(0, max);
+    if (adjust) return (current + param).clamp(0, max).toDouble();
     return current + (param > 0 ? max - current : current) * (param / 100);
   }
 
-  int updateRgb(int current, num? param) =>
-      fuzzyRound(updateValue(current, param, 255));
+  int updateRgb(int current, double? param) =>
+      fuzzyRound(updateValue(current.toDouble(), param, 255));
 
   if (hasRgb) {
     return color.changeRgb(
@@ -789,8 +789,8 @@ bool _isVarSlash(Value value) =>
 /// within `0` and [max]. Otherwise, this throws a [SassScriptException].
 ///
 /// [name] is used to identify the argument in the error message.
-num _percentageOrUnitless(SassNumber number, num max, String name) {
-  num value;
+double _percentageOrUnitless(SassNumber number, num max, String name) {
+  double value;
   if (!number.hasUnits) {
     value = number.value;
   } else if (number.hasUnit("%")) {
@@ -800,7 +800,7 @@ num _percentageOrUnitless(SassNumber number, num max, String name) {
         '\$$name: Expected $number to have no units or "%".');
   }
 
-  return value.clamp(0, max);
+  return value.clamp(0, max).toDouble();
 }
 
 /// Returns [color1] and [color2], mixed together and weighted by [weight].
diff --git a/lib/src/functions/math.dart b/lib/src/functions/math.dart
index 44f1948ab..d0b0f151c 100644
--- a/lib/src/functions/math.dart
+++ b/lib/src/functions/math.dart
@@ -11,7 +11,6 @@ import '../callable.dart';
 import '../evaluation_context.dart';
 import '../exception.dart';
 import '../module/built_in.dart';
-import '../util/number.dart';
 import '../value.dart';
 
 /// The global definitions of Sass math functions.
@@ -30,13 +29,18 @@ final module = BuiltInModule("math", functions: [
 ], variables: {
   "e": SassNumber(math.e),
   "pi": SassNumber(math.pi),
+  "epsilon": SassNumber(2.220446049250313e-16),
+  "max-safe-integer": SassNumber(9007199254740991),
+  "min-safe-integer": SassNumber(-9007199254740991),
+  "max-number": SassNumber(double.maxFinite),
+  "min-number": SassNumber(double.minPositive),
 });
 
 ///
 /// Bounding functions
 ///
 
-final _ceil = _numberFunction("ceil", (value) => value.ceil());
+final _ceil = _numberFunction("ceil", (value) => value.ceil().toDouble());
 
 final _clamp = _function("clamp", r"$min, $number, $max", (arguments) {
   var min = arguments[0].assertNumber("min");
@@ -55,7 +59,7 @@ final _clamp = _function("clamp", r"$min, $number, $max", (arguments) {
   return number;
 });
 
-final _floor = _numberFunction("floor", (value) => value.floor());
+final _floor = _numberFunction("floor", (value) => value.floor().toDouble());
 
 final _max = _function("max", r"$numbers...", (arguments) {
   SassNumber? max;
@@ -77,7 +81,7 @@ final _min = _function("min", r"$numbers...", (arguments) {
   throw SassScriptException("At least one argument must be passed.");
 });
 
-final _round = _numberFunction("round", fuzzyRound);
+final _round = _numberFunction("round", (number) => number.round().toDouble());
 
 ///
 /// Distance functions
@@ -112,20 +116,16 @@ final _log = _function("log", r"$number, $base: null", (arguments) {
   var number = arguments[0].assertNumber("number");
   if (number.hasUnits) {
     throw SassScriptException("\$number: Expected $number to have no units.");
+  } else if (arguments[1] == sassNull) {
+    return SassNumber(math.log(number.value));
   }
 
-  var numberValue = _fuzzyRoundIfZero(number.value);
-  if (arguments[1] == sassNull) return SassNumber(math.log(numberValue));
-
   var base = arguments[1].assertNumber("base");
   if (base.hasUnits) {
     throw SassScriptException("\$base: Expected $base to have no units.");
+  } else {
+    return SassNumber(math.log(number.value) / math.log(base.value));
   }
-
-  var baseValue = fuzzyEquals(base.value, 1)
-      ? fuzzyRound(base.value)
-      : _fuzzyRoundIfZero(base.value);
-  return SassNumber(math.log(numberValue) / math.log(baseValue));
 });
 
 final _pow = _function("pow", r"$base, $exponent", (arguments) {
@@ -136,45 +136,18 @@ final _pow = _function("pow", r"$base, $exponent", (arguments) {
   } else if (exponent.hasUnits) {
     throw SassScriptException(
         "\$exponent: Expected $exponent to have no units.");
+  } else {
+    return SassNumber(math.pow(base.value, exponent.value));
   }
-
-  // Exponentiating certain real numbers leads to special behaviors. Ensure that
-  // these behaviors are consistent for numbers within the precision limit.
-  var baseValue = _fuzzyRoundIfZero(base.value);
-  var exponentValue = _fuzzyRoundIfZero(exponent.value);
-  if (fuzzyEquals(baseValue.abs(), 1) && exponentValue.isInfinite) {
-    return SassNumber(double.nan);
-  } else if (fuzzyEquals(baseValue, 0)) {
-    if (exponentValue.isFinite) {
-      var intExponent = fuzzyAsInt(exponentValue);
-      if (intExponent != null && intExponent % 2 == 1) {
-        exponentValue = fuzzyRound(exponentValue);
-      }
-    }
-  } else if (baseValue.isFinite &&
-      fuzzyLessThan(baseValue, 0) &&
-      exponentValue.isFinite &&
-      fuzzyIsInt(exponentValue)) {
-    exponentValue = fuzzyRound(exponentValue);
-  } else if (baseValue.isInfinite &&
-      fuzzyLessThan(baseValue, 0) &&
-      exponentValue.isFinite) {
-    var intExponent = fuzzyAsInt(exponentValue);
-    if (intExponent != null && intExponent % 2 == 1) {
-      exponentValue = fuzzyRound(exponentValue);
-    }
-  }
-  return SassNumber(math.pow(baseValue, exponentValue));
 });
 
 final _sqrt = _function("sqrt", r"$number", (arguments) {
   var number = arguments[0].assertNumber("number");
   if (number.hasUnits) {
     throw SassScriptException("\$number: Expected $number to have no units.");
+  } else {
+    return SassNumber(math.sqrt(number.value));
   }
-
-  var numberValue = _fuzzyRoundIfZero(number.value);
-  return SassNumber(math.sqrt(numberValue));
 });
 
 ///
@@ -185,75 +158,60 @@ final _acos = _function("acos", r"$number", (arguments) {
   var number = arguments[0].assertNumber("number");
   if (number.hasUnits) {
     throw SassScriptException("\$number: Expected $number to have no units.");
+  } else {
+    return SassNumber.withUnits(math.acos(number.value) * 180 / math.pi,
+        numeratorUnits: ['deg']);
   }
-
-  var numberValue = fuzzyEquals(number.value.abs(), 1)
-      ? fuzzyRound(number.value)
-      : number.value;
-  var acos = math.acos(numberValue) * 180 / math.pi;
-  return SassNumber.withUnits(acos, numeratorUnits: ['deg']);
 });
 
 final _asin = _function("asin", r"$number", (arguments) {
   var number = arguments[0].assertNumber("number");
   if (number.hasUnits) {
     throw SassScriptException("\$number: Expected $number to have no units.");
+  } else {
+    return SassNumber.withUnits(math.asin(number.value) * 180 / math.pi,
+        numeratorUnits: ['deg']);
   }
-
-  var numberValue = fuzzyEquals(number.value.abs(), 1)
-      ? fuzzyRound(number.value)
-      : _fuzzyRoundIfZero(number.value);
-  var asin = math.asin(numberValue) * 180 / math.pi;
-  return SassNumber.withUnits(asin, numeratorUnits: ['deg']);
 });
 
 final _atan = _function("atan", r"$number", (arguments) {
   var number = arguments[0].assertNumber("number");
   if (number.hasUnits) {
     throw SassScriptException("\$number: Expected $number to have no units.");
+  } else {
+    return SassNumber.withUnits(math.atan(number.value) * 180 / math.pi,
+        numeratorUnits: ['deg']);
   }
-
-  var numberValue = _fuzzyRoundIfZero(number.value);
-  var atan = math.atan(numberValue) * 180 / math.pi;
-  return SassNumber.withUnits(atan, numeratorUnits: ['deg']);
 });
 
 final _atan2 = _function("atan2", r"$y, $x", (arguments) {
   var y = arguments[0].assertNumber("y");
   var x = arguments[1].assertNumber("x");
-
-  var xValue = _fuzzyRoundIfZero(x.convertValueToMatch(y, 'x', 'y'));
-  var yValue = _fuzzyRoundIfZero(y.value);
-  var atan2 = math.atan2(yValue, xValue) * 180 / math.pi;
-  return SassNumber.withUnits(atan2, numeratorUnits: ['deg']);
-});
-
-final _cos = _function("cos", r"$number", (arguments) {
-  var value =
-      arguments[0].assertNumber("number").coerceValueToUnit("rad", "number");
-  return SassNumber(math.cos(value));
-});
-
-final _sin = _function("sin", r"$number", (arguments) {
-  var value = _fuzzyRoundIfZero(
-      arguments[0].assertNumber("number").coerceValueToUnit("rad", "number"));
-  return SassNumber(math.sin(value));
+  return SassNumber.withUnits(
+      math.atan2(y.value, x.convertValueToMatch(y, 'x', 'y')) * 180 / math.pi,
+      numeratorUnits: ['deg']);
 });
 
-final _tan = _function("tan", r"$number", (arguments) {
-  var value =
-      arguments[0].assertNumber("number").coerceValueToUnit("rad", "number");
-  var asymptoteInterval = 0.5 * math.pi;
-  var tanPeriod = 2 * math.pi;
-  if (fuzzyEquals((value - asymptoteInterval) % tanPeriod, 0)) {
-    return SassNumber(double.infinity);
-  } else if (fuzzyEquals((value + asymptoteInterval) % tanPeriod, 0)) {
-    return SassNumber(double.negativeInfinity);
-  } else {
-    var numberValue = _fuzzyRoundIfZero(value);
-    return SassNumber(math.tan(numberValue));
-  }
-});
+final _cos = _function(
+    "cos",
+    r"$number",
+    (arguments) => SassNumber(math.cos(arguments[0]
+        .assertNumber("number")
+        .coerceValueToUnit("rad", "number"))));
+
+final _sin = _function(
+    "sin",
+    r"$number",
+    (arguments) => SassNumber(math.sin(arguments[0]
+        .assertNumber("number")
+        .coerceValueToUnit("rad", "number"))));
+
+final _tan = _function(
+    "tan",
+    r"$number",
+    (arguments) => SassNumber(math.tan(arguments[0]
+        .assertNumber("number")
+        .coerceValueToUnit("rad", "number"))));
 
 ///
 /// Unit functions
@@ -329,14 +287,9 @@ final _div = _function("div", r"$number1, $number2", (arguments) {
 /// Helpers
 ///
 
-num _fuzzyRoundIfZero(num number) {
-  if (!fuzzyEquals(number, 0)) return number;
-  return number.isNegative ? -0.0 : 0;
-}
-
 /// Returns a [Callable] named [name] that transforms a number's value
 /// using [transform] and preserves its units.
-BuiltInCallable _numberFunction(String name, num transform(num value)) {
+BuiltInCallable _numberFunction(String name, double transform(double value)) {
   return _function(name, r"$number", (arguments) {
     var number = arguments[0].assertNumber("number");
     return SassNumber.withUnits(transform(number.value),
diff --git a/lib/src/node/legacy/value/color.dart b/lib/src/node/legacy/value/color.dart
index fe5fcbf5c..6aae64426 100644
--- a/lib/src/node/legacy/value/color.dart
+++ b/lib/src/node/legacy/value/color.dart
@@ -4,6 +4,7 @@
 
 import 'package:js/js.dart';
 
+import '../../../util/number.dart';
 import '../../../value.dart';
 import '../../reflection.dart';
 
@@ -68,4 +69,4 @@ final JSClass legacyColorClass = createJSClass('sass.types.Color',
 
 /// Clamps [channel] within the range 0, 255 and rounds it to the nearest
 /// integer.
-int _clamp(num channel) => channel.clamp(0, 255).round();
+int _clamp(num channel) => fuzzyRound(channel.clamp(0, 255));
diff --git a/lib/src/parse/parser.dart b/lib/src/parse/parser.dart
index 16f01bd89..58c1e73e1 100644
--- a/lib/src/parse/parser.dart
+++ b/lib/src/parse/parser.dart
@@ -261,17 +261,18 @@ class Parser {
     return buffer.toString();
   }
 
-  /// Consumes and returns a natural number (that is, a non-negative integer).
+  /// Consumes and returns a natural number (that is, a non-negative integer) as
+  /// a double.
   ///
   /// Doesn't support scientific notation.
   @protected
-  int naturalNumber() {
+  double naturalNumber() {
     var first = scanner.readChar();
     if (!isDigit(first)) {
       scanner.error("Expected digit.", position: scanner.position - 1);
     }
 
-    var number = asDecimal(first);
+    var number = asDecimal(first).toDouble();
     while (isDigit(scanner.peekChar())) {
       number *= 10;
       number += asDecimal(scanner.readChar());
diff --git a/lib/src/parse/stylesheet.dart b/lib/src/parse/stylesheet.dart
index a76bef0e4..c1326af59 100644
--- a/lib/src/parse/stylesheet.dart
+++ b/lib/src/parse/stylesheet.dart
@@ -2,8 +2,6 @@
 // MIT-style license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-import 'dart:math' as math;
-
 import 'package:charcode/charcode.dart';
 import 'package:meta/meta.dart';
 import 'package:path/path.dart' as p;
@@ -2412,7 +2410,7 @@ abstract class StylesheetParser extends Parser {
     int red;
     int green;
     int blue;
-    num? alpha;
+    double? alpha;
     if (!isHex(scanner.peekChar())) {
       // #abc
       red = (digit1 << 4) + digit1;
@@ -2530,16 +2528,19 @@ abstract class StylesheetParser extends Parser {
   NumberExpression _number() {
     var start = scanner.state;
     var first = scanner.peekChar();
-    var sign = first == $minus ? -1 : 1;
     if (first == $plus || first == $minus) scanner.readChar();
 
-    num number = scanner.peekChar() == $dot ? 0 : naturalNumber();
+    if (scanner.peekChar() != $dot) _consumeNaturalNumber();
 
     // Don't complain about a dot after a number unless the number starts with a
     // dot. We don't allow a plain ".", but we need to allow "1." so that
     // "1..." will work as a rest argument.
-    number += _tryDecimal(allowTrailingDot: scanner.position != start.position);
-    number *= _tryExponent();
+    _tryDecimal(allowTrailingDot: scanner.position != start.position);
+    _tryExponent();
+
+    // Use Dart's built-in double parsing so that we don't accumulate
+    // floating-point errors for numbers with lots of digits.
+    var number = double.parse(scanner.substring(start.position));
 
     String? unit;
     if (scanner.scanChar($percent)) {
@@ -2550,21 +2551,32 @@ abstract class StylesheetParser extends Parser {
       unit = identifier(unit: true);
     }
 
-    return NumberExpression(sign * number, scanner.spanFrom(start), unit: unit);
+    return NumberExpression(number, scanner.spanFrom(start), unit: unit);
   }
 
-  /// Consumes the decimal component of a number and returns its value, or 0 if
-  /// there is no decimal component.
+  /// Consumes a natural number (that is, a non-negative integer).
+  ///
+  /// Doesn't support scientific notation.
+  void _consumeNaturalNumber() {
+    if (!isDigit(scanner.readChar())) {
+      scanner.error("Expected digit.", position: scanner.position - 1);
+    }
+
+    while (isDigit(scanner.peekChar())) {
+      scanner.readChar();
+    }
+  }
+
+  /// Consumes the decimal component of a number if it exists.
   ///
   /// If [allowTrailingDot] is `false`, this will throw an error if there's a
   /// dot without any numbers following it. Otherwise, it will ignore the dot
   /// without consuming it.
-  num _tryDecimal({bool allowTrailingDot = false}) {
-    var start = scanner.position;
-    if (scanner.peekChar() != $dot) return 0;
+  void _tryDecimal({bool allowTrailingDot = false}) {
+    if (scanner.peekChar() != $dot) return;
 
     if (!isDigit(scanner.peekChar(1))) {
-      if (allowTrailingDot) return 0;
+      if (allowTrailingDot) return;
       scanner.error("Expected digit.", position: scanner.position + 1);
     }
 
@@ -2572,33 +2584,23 @@ abstract class StylesheetParser extends Parser {
     while (isDigit(scanner.peekChar())) {
       scanner.readChar();
     }
-
-    // Use Dart's built-in double parsing so that we don't accumulate
-    // floating-point errors for numbers with lots of digits.
-    return double.parse(scanner.substring(start));
   }
 
-  /// Consumes the exponent component of a number and returns its value, or 1 if
-  /// there is no exponent component.
-  num _tryExponent() {
+  /// Consumes the exponent component of a number if it exists.
+  void _tryExponent() {
     var first = scanner.peekChar();
-    if (first != $e && first != $E) return 1;
+    if (first != $e && first != $E) return;
 
     var next = scanner.peekChar(1);
-    if (!isDigit(next) && next != $minus && next != $plus) return 1;
+    if (!isDigit(next) && next != $minus && next != $plus) return;
 
     scanner.readChar();
-    var exponentSign = next == $minus ? -1 : 1;
     if (next == $plus || next == $minus) scanner.readChar();
     if (!isDigit(scanner.peekChar())) scanner.error("Expected digit.");
 
-    var exponent = 0.0;
     while (isDigit(scanner.peekChar())) {
-      exponent *= 10;
-      exponent += scanner.readChar() - $0;
+      scanner.readChar();
     }
-
-    return math.pow(10, exponentSign * exponent);
   }
 
   /// Consumes a unicode range expression.
diff --git a/lib/src/util/number.dart b/lib/src/util/number.dart
index c47ab44da..80fd3aaa2 100644
--- a/lib/src/util/number.dart
+++ b/lib/src/util/number.dart
@@ -6,22 +6,35 @@ import 'dart:math' as math;
 
 import '../value.dart';
 
-/// The maximum distance two Sass numbers are allowed to be from one another
-/// before they're considered different.
-final epsilon = math.pow(10, -SassNumber.precision - 1);
-
-/// Returns whether [number1] and [number2] are equal within [epsilon].
-bool fuzzyEquals(num number1, num number2) =>
-    (number1 - number2).abs() < epsilon;
+/// The power of ten to which to round Sass numbers to determine if they're
+/// [fuzzy equal] to one another
+///
+/// [fuzzy-equal]: https://github.com/sass/sass/blob/main/spec/types/number.md#fuzzy-equality
+///
+/// This is also the minimum distance such that `a - b > _epsilon` implies that
+/// `a` isn't [fuzzy-equal] to `b`. Note that the inverse implication is not
+/// necessarily true! For example, if `a = 5.1e-11` and `b = 4.4e-11`, then
+/// `a - b < 1e-11` but `a` fuzzy-equals 5e-11 and b fuzzy-equals 4e-11.
+final _epsilon = math.pow(10, -SassNumber.precision - 1);
 
-/// `1 / epsilon`, cached since [math.pow] may not be computed at compile-time
+/// `1 / _epsilon`, cached since [math.pow] may not be computed at compile-time
 /// and thus this probably won't be constant-folded.
-final _inverseEpsilon = 1 / epsilon;
+final _inverseEpsilon = math.pow(10, SassNumber.precision + 1);
+
+/// Returns whether [number1] and [number2] are equal up to the 11th decimal
+/// digit.
+bool fuzzyEquals(num number1, num number2) {
+  if (number1 == number2) return true;
+  return (number1 - number2).abs() <= _epsilon &&
+      (number1 * _inverseEpsilon).round() ==
+          (number2 * _inverseEpsilon).round();
+}
 
 /// Returns a hash code for [number] that matches [fuzzyEquals].
-int fuzzyHashCode(num number) => number.isInfinite || number.isNaN
-    ? number.hashCode
-    : (number * _inverseEpsilon).round().hashCode;
+int fuzzyHashCode(double number) {
+  if (!number.isFinite) return number.hashCode;
+  return (number * _inverseEpsilon).round().hashCode;
+}
 
 /// Returns whether [number1] is less than [number2], and not [fuzzyEquals].
 bool fuzzyLessThan(num number1, num number2) =>
@@ -40,21 +53,20 @@ bool fuzzyGreaterThanOrEquals(num number1, num number2) =>
     number1 > number2 || fuzzyEquals(number1, number2);
 
 /// Returns whether [number] is [fuzzyEquals] to an integer.
-bool fuzzyIsInt(num number) {
-  // Check this before is int to work around dart-lang/sdk#43325.
+bool fuzzyIsInt(double number) {
   if (number.isInfinite || number.isNaN) return false;
-  if (number is int) return true;
-
-  // Check against 0.5 rather than 0.0 so that we catch numbers that are both
-  // very slightly above an integer, and very slightly below.
-  return fuzzyEquals((number - 0.5).abs() % 1, 0.5);
+  return fuzzyEquals(number, number.round());
 }
 
 /// If [number] is an integer according to [fuzzyIsInt], returns it as an
 /// [int].
 ///
 /// Otherwise, returns `null`.
-int? fuzzyAsInt(num number) => fuzzyIsInt(number) ? number.round() : null;
+int? fuzzyAsInt(double number) {
+  if (number.isInfinite || number.isNaN) return null;
+  var rounded = number.round();
+  return fuzzyEquals(number, rounded) ? rounded : null;
+}
 
 /// Rounds [number] to the nearest integer.
 ///
@@ -75,9 +87,9 @@ int fuzzyRound(num number) {
 ///
 /// If [number] is [fuzzyEquals] to [min] or [max], it's clamped to the
 /// appropriate value.
-num? fuzzyCheckRange(num number, num min, num max) {
-  if (fuzzyEquals(number, min)) return min;
-  if (fuzzyEquals(number, max)) return max;
+double? fuzzyCheckRange(double number, num min, num max) {
+  if (fuzzyEquals(number, min)) return min.toDouble();
+  if (fuzzyEquals(number, max)) return max.toDouble();
   if (number > min && number < max) return number;
   return null;
 }
@@ -86,9 +98,23 @@ num? fuzzyCheckRange(num number, num min, num max) {
 ///
 /// If [number] is [fuzzyEquals] to [min] or [max], it's clamped to the
 /// appropriate value. [name] is used in error reporting.
-num fuzzyAssertRange(num number, int min, int max, [String? name]) {
+double fuzzyAssertRange(double number, int min, int max, [String? name]) {
   var result = fuzzyCheckRange(number, min, max);
   if (result != null) return result;
   throw RangeError.range(
       number, min, max, name, "must be between $min and $max");
 }
+
+/// Return [num1] modulo [num2], using Sass's [floored division] modulo
+/// semantics, which it inherited from Ruby and which differ from Dart's.
+///
+/// [floored division]: https://en.wikipedia.org/wiki/Modulo_operation#Variants_of_the_definition
+double moduloLikeSass(double num1, double num2) {
+  if (num2 > 0) return num1 % num2;
+  if (num2 == 0) return double.nan;
+
+  // Dart has different mod-negative semantics than Ruby, and thus than
+  // Sass.
+  var result = num1 % num2;
+  return result == 0 ? 0 : result + num2;
+}
diff --git a/lib/src/value.dart b/lib/src/value.dart
index 23197ff43..fef8881c8 100644
--- a/lib/src/value.dart
+++ b/lib/src/value.dart
@@ -410,7 +410,8 @@ extension SassApiValue on Value {
       // TODO(nweiz): colorize this if we're running in an environment where
       // that works.
       throwWithTrace(
-          SassScriptException(error.toString().replaceFirst("Error: ", ""), name),
+          SassScriptException(
+              error.toString().replaceFirst("Error: ", ""), name),
           stackTrace);
     }
   }
@@ -433,7 +434,8 @@ extension SassApiValue on Value {
       // TODO(nweiz): colorize this if we're running in an environment where
       // that works.
       throwWithTrace(
-          SassScriptException(error.toString().replaceFirst("Error: ", ""), name),
+          SassScriptException(
+              error.toString().replaceFirst("Error: ", ""), name),
           stackTrace);
     }
   }
@@ -456,7 +458,8 @@ extension SassApiValue on Value {
       // TODO(nweiz): colorize this if we're running in an environment where
       // that works.
       throwWithTrace(
-          SassScriptException(error.toString().replaceFirst("Error: ", ""), name),
+          SassScriptException(
+              error.toString().replaceFirst("Error: ", ""), name),
           stackTrace);
     }
   }
@@ -479,7 +482,8 @@ extension SassApiValue on Value {
       // TODO(nweiz): colorize this if we're running in an environment where
       // that works.
       throwWithTrace(
-          SassScriptException(error.toString().replaceFirst("Error: ", ""), name),
+          SassScriptException(
+              error.toString().replaceFirst("Error: ", ""), name),
           stackTrace);
     }
   }
diff --git a/lib/src/value/calculation.dart b/lib/src/value/calculation.dart
index 209ad7a8d..d52e5d283 100644
--- a/lib/src/value/calculation.dart
+++ b/lib/src/value/calculation.dart
@@ -235,7 +235,8 @@ class SassCalculation extends Value {
       return arg;
     } else if (arg is SassString) {
       if (!arg.hasQuotes) return arg;
-      throw SassScriptException("Quoted string $arg can't be used in a calculation.");
+      throw SassScriptException(
+          "Quoted string $arg can't be used in a calculation.");
     } else if (arg is SassCalculation) {
       return arg.name == 'calc' ? arg.arguments[0] : arg;
     } else if (arg is Value) {
@@ -255,7 +256,8 @@ class SassCalculation extends Value {
     for (var arg in args) {
       if (arg is! SassNumber) continue;
       if (arg.numeratorUnits.length > 1 || arg.denominatorUnits.isNotEmpty) {
-        throw SassScriptException("Number $arg isn't compatible with CSS calculations.");
+        throw SassScriptException(
+            "Number $arg isn't compatible with CSS calculations.");
       }
     }
 
diff --git a/lib/src/value/color.dart b/lib/src/value/color.dart
index 02e03477c..3d3db20f2 100644
--- a/lib/src/value/color.dart
+++ b/lib/src/value/color.dart
@@ -42,31 +42,31 @@ class SassColor extends Value {
   int? _blue;
 
   /// This color's hue, between `0` and `360`.
-  num get hue {
+  double get hue {
     if (_hue == null) _rgbToHsl();
     return _hue!;
   }
 
-  num? _hue;
+  double? _hue;
 
   /// This color's saturation, a percentage between `0` and `100`.
-  num get saturation {
+  double get saturation {
     if (_saturation == null) _rgbToHsl();
     return _saturation!;
   }
 
-  num? _saturation;
+  double? _saturation;
 
   /// This color's lightness, a percentage between `0` and `100`.
-  num get lightness {
+  double get lightness {
     if (_lightness == null) _rgbToHsl();
     return _lightness!;
   }
 
-  num? _lightness;
+  double? _lightness;
 
   /// This color's whiteness, a percentage between `0` and `100`.
-  num get whiteness {
+  double get whiteness {
     // Because HWB is (currently) used much less frequently than HSL or RGB, we
     // don't cache its values because we expect the memory overhead of doing so
     // to outweigh the cost of recalculating it on access.
@@ -74,7 +74,7 @@ class SassColor extends Value {
   }
 
   /// This color's blackness, a percentage between `0` and `100`.
-  num get blackness {
+  double get blackness {
     // Because HWB is (currently) used much less frequently than HSL or RGB, we
     // don't cache its values because we expect the memory overhead of doing so
     // to outweigh the cost of recalculating it on access.
@@ -85,8 +85,8 @@ class SassColor extends Value {
   // the same name in the JS API.
 
   /// This color's alpha channel, between `0` and `1`.
-  num get alpha => _alpha;
-  final num _alpha;
+  double get alpha => _alpha;
+  final double _alpha;
 
   /// The format in which this color was originally written and should be
   /// serialized in expanded mode, or `null` if the color wasn't written in a
@@ -109,7 +109,9 @@ class SassColor extends Value {
   @internal
   SassColor.rgbInternal(this._red, this._green, this._blue,
       [num? alpha, this.format])
-      : _alpha = alpha == null ? 1 : fuzzyAssertRange(alpha, 0, 1, "alpha") {
+      : _alpha = alpha == null
+            ? 1
+            : fuzzyAssertRange(alpha.toDouble(), 0, 1, "alpha") {
     RangeError.checkValueInInterval(red, 0, 255, "red");
     RangeError.checkValueInInterval(green, 0, 255, "green");
     RangeError.checkValueInInterval(blue, 0, 255, "blue");
@@ -129,9 +131,13 @@ class SassColor extends Value {
   SassColor.hslInternal(num hue, num saturation, num lightness,
       [num? alpha, this.format])
       : _hue = hue % 360,
-        _saturation = fuzzyAssertRange(saturation, 0, 100, "saturation"),
-        _lightness = fuzzyAssertRange(lightness, 0, 100, "lightness"),
-        _alpha = alpha == null ? 1 : fuzzyAssertRange(alpha, 0, 1, "alpha");
+        _saturation =
+            fuzzyAssertRange(saturation.toDouble(), 0, 100, "saturation"),
+        _lightness =
+            fuzzyAssertRange(lightness.toDouble(), 0, 100, "lightness"),
+        _alpha = alpha == null
+            ? 1
+            : fuzzyAssertRange(alpha.toDouble(), 0, 1, "alpha");
 
   /// Creates an HWB color.
   ///
@@ -141,9 +147,9 @@ class SassColor extends Value {
     // From https://www.w3.org/TR/css-color-4/#hwb-to-rgb
     var scaledHue = hue % 360 / 360;
     var scaledWhiteness =
-        fuzzyAssertRange(whiteness, 0, 100, "whiteness") / 100;
+        fuzzyAssertRange(whiteness.toDouble(), 0, 100, "whiteness") / 100;
     var scaledBlackness =
-        fuzzyAssertRange(blackness, 0, 100, "blackness") / 100;
+        fuzzyAssertRange(blackness.toDouble(), 0, 100, "blackness") / 100;
 
     var sum = scaledWhiteness + scaledBlackness;
     if (sum > 1) {
@@ -152,7 +158,7 @@ class SassColor extends Value {
     }
 
     var factor = 1 - scaledWhiteness - scaledBlackness;
-    int toRgb(num hue) {
+    int toRgb(double hue) {
       var channel = _hueToRgb(0, 1, hue) * factor + scaledWhiteness;
       return fuzzyRound(channel * 255);
     }
@@ -192,8 +198,14 @@ class SassColor extends Value {
           blackness ?? this.blackness, alpha ?? this.alpha);
 
   /// Returns a new copy of this color with the alpha channel set to [alpha].
-  SassColor changeAlpha(num alpha) => SassColor._(_red, _green, _blue, _hue,
-      _saturation, _lightness, fuzzyAssertRange(alpha, 0, 1, "alpha"));
+  SassColor changeAlpha(num alpha) => SassColor._(
+      _red,
+      _green,
+      _blue,
+      _hue,
+      _saturation,
+      _lightness,
+      fuzzyAssertRange(alpha.toDouble(), 0, 1, "alpha"));
 
   /// @nodoc
   @internal
@@ -282,7 +294,7 @@ class SassColor extends Value {
 
   /// An algorithm from the CSS3 spec:
   /// http://www.w3.org/TR/css3-color/#hsl-color.
-  static num _hueToRgb(num m1, num m2, num hue) {
+  static double _hueToRgb(double m1, double m2, double hue) {
     if (hue < 0) hue += 1;
     if (hue > 1) hue -= 1;
 
diff --git a/lib/src/value/number.dart b/lib/src/value/number.dart
index e4448059e..e57e8e303 100644
--- a/lib/src/value/number.dart
+++ b/lib/src/value/number.dart
@@ -22,7 +22,7 @@ import 'number/unitless.dart';
 const _conversions = {
   // Length
   "in": {
-    "in": 1,
+    "in": 1.0,
     "cm": 1 / 2.54,
     "pc": 1 / 6,
     "mm": 1 / 25.4,
@@ -32,7 +32,7 @@ const _conversions = {
   },
   "cm": {
     "in": 2.54,
-    "cm": 1,
+    "cm": 1.0,
     "pc": 2.54 / 6,
     "mm": 1 / 10,
     "q": 1 / 40,
@@ -40,9 +40,9 @@ const _conversions = {
     "px": 2.54 / 96,
   },
   "pc": {
-    "in": 6,
+    "in": 6.0,
     "cm": 6 / 2.54,
-    "pc": 1,
+    "pc": 1.0,
     "mm": 6 / 25.4,
     "q": 6 / 101.6,
     "pt": 1 / 12,
@@ -50,96 +50,96 @@ const _conversions = {
   },
   "mm": {
     "in": 25.4,
-    "cm": 10,
+    "cm": 10.0,
     "pc": 25.4 / 6,
-    "mm": 1,
+    "mm": 1.0,
     "q": 1 / 4,
     "pt": 25.4 / 72,
     "px": 25.4 / 96,
   },
   "q": {
     "in": 101.6,
-    "cm": 40,
+    "cm": 40.0,
     "pc": 101.6 / 6,
-    "mm": 4,
-    "q": 1,
+    "mm": 4.0,
+    "q": 1.0,
     "pt": 101.6 / 72,
     "px": 101.6 / 96,
   },
   "pt": {
-    "in": 72,
+    "in": 72.0,
     "cm": 72 / 2.54,
-    "pc": 12,
+    "pc": 12.0,
     "mm": 72 / 25.4,
     "q": 72 / 101.6,
-    "pt": 1,
+    "pt": 1.0,
     "px": 3 / 4,
   },
   "px": {
-    "in": 96,
+    "in": 96.0,
     "cm": 96 / 2.54,
-    "pc": 16,
+    "pc": 16.0,
     "mm": 96 / 25.4,
     "q": 96 / 101.6,
     "pt": 4 / 3,
-    "px": 1,
+    "px": 1.0,
   },
 
   // Rotation
   "deg": {
-    "deg": 1,
+    "deg": 1.0,
     "grad": 9 / 10,
     "rad": 180 / pi,
-    "turn": 360,
+    "turn": 360.0,
   },
   "grad": {
     "deg": 10 / 9,
-    "grad": 1,
+    "grad": 1.0,
     "rad": 200 / pi,
-    "turn": 400,
+    "turn": 400.0,
   },
   "rad": {
     "deg": pi / 180,
     "grad": pi / 200,
-    "rad": 1,
+    "rad": 1.0,
     "turn": 2 * pi,
   },
   "turn": {
     "deg": 1 / 360,
     "grad": 1 / 400,
     "rad": 1 / (2 * pi),
-    "turn": 1,
+    "turn": 1.0,
   },
 
   // Time
   "s": {
-    "s": 1,
+    "s": 1.0,
     "ms": 1 / 1000,
   },
   "ms": {
-    "s": 1000,
-    "ms": 1,
+    "s": 1000.0,
+    "ms": 1.0,
   },
 
   // Frequency
-  "Hz": {"Hz": 1, "kHz": 1000},
-  "kHz": {"Hz": 1 / 1000, "kHz": 1},
+  "Hz": {"Hz": 1.0, "kHz": 1000.0},
+  "kHz": {"Hz": 1 / 1000, "kHz": 1.0},
 
   // Pixel density
   "dpi": {
-    "dpi": 1,
+    "dpi": 1.0,
     "dpcm": 2.54,
-    "dppx": 96,
+    "dppx": 96.0,
   },
   "dpcm": {
     "dpi": 1 / 2.54,
-    "dpcm": 1,
+    "dpcm": 1.0,
     "dppx": 96 / 2.54,
   },
   "dppx": {
     "dpi": 1 / 96,
     "dpcm": 2.54 / 96,
-    "dppx": 1,
+    "dppx": 1.0,
   },
 };
 
@@ -165,7 +165,7 @@ final _typesByUnit = {
 ///
 /// @nodoc
 @internal
-num? conversionFactor(String unit1, String unit2) {
+double? conversionFactor(String unit1, String unit2) {
   if (unit1 == unit2) return 1;
   var innerMap = _conversions[unit1];
   if (innerMap == null) return null;
@@ -191,12 +191,12 @@ abstract class SassNumber extends Value {
 
   /// The value of this number.
   ///
-  /// Note that due to details of floating-point arithmetic, this may be a
-  /// [double] even if [this] represents an int from Sass's perspective. Use
-  /// [isInt] to determine whether this is an integer, [asInt] to get its
-  /// integer value, or [assertInt] to do both at once.
-  num get value => _value;
-  final num _value;
+  /// Note that Sass stores all numbers as [double]s even if if [this]
+  /// represents an integer from Sass's perspective. Use [isInt] to determine
+  /// whether this is an integer, [asInt] to get its integer value, or
+  /// [assertInt] to do both at once.
+  double get value => _value;
+  final double _value;
 
   /// The cached hash code for this number, if it's been computed.
   ///
@@ -246,24 +246,25 @@ abstract class SassNumber extends Value {
   /// This matches the numbers that can be written as literals.
   /// [SassNumber.withUnits] can be used to construct more complex units.
   factory SassNumber(num value, [String? unit]) => unit == null
-      ? UnitlessSassNumber(value)
-      : SingleUnitSassNumber(value, unit);
+      ? UnitlessSassNumber(value.toDouble())
+      : SingleUnitSassNumber(value.toDouble(), unit);
 
   /// Creates a number with full [numeratorUnits] and [denominatorUnits].
   factory SassNumber.withUnits(num value,
       {List<String>? numeratorUnits, List<String>? denominatorUnits}) {
+    var valueDouble = value.toDouble();
     if (denominatorUnits == null || denominatorUnits.isEmpty) {
       if (numeratorUnits == null || numeratorUnits.isEmpty) {
-        return UnitlessSassNumber(value);
+        return UnitlessSassNumber(valueDouble);
       } else if (numeratorUnits.length == 1) {
-        return SingleUnitSassNumber(value, numeratorUnits[0]);
+        return SingleUnitSassNumber(valueDouble, numeratorUnits[0]);
       } else {
         return ComplexSassNumber(
-            value, List.unmodifiable(numeratorUnits), const []);
+            valueDouble, List.unmodifiable(numeratorUnits), const []);
       }
     } else if (numeratorUnits == null || numeratorUnits.isEmpty) {
       return ComplexSassNumber(
-          value, const [], List.unmodifiable(denominatorUnits));
+          valueDouble, const [], List.unmodifiable(denominatorUnits));
     } else {
       var numerators = numeratorUnits.toList();
       var unsimplifiedDenominators = denominatorUnits.toList();
@@ -274,7 +275,7 @@ abstract class SassNumber extends Value {
         for (var i = 0; i < numerators.length; i++) {
           var factor = conversionFactor(denominator, numerators[i]);
           if (factor == null) continue;
-          value *= factor;
+          valueDouble *= factor;
           numerators.removeAt(i);
           simplifiedAway = true;
           break;
@@ -284,13 +285,13 @@ abstract class SassNumber extends Value {
 
       if (denominatorUnits.isEmpty) {
         if (numeratorUnits.isEmpty) {
-          return UnitlessSassNumber(value);
+          return UnitlessSassNumber(valueDouble);
         } else if (numeratorUnits.length == 1) {
-          return SingleUnitSassNumber(value, numeratorUnits.single);
+          return SingleUnitSassNumber(valueDouble, numeratorUnits.single);
         }
       }
 
-      return ComplexSassNumber(value, List.unmodifiable(numerators),
+      return ComplexSassNumber(valueDouble, List.unmodifiable(numerators),
           List.unmodifiable(denominators));
     }
   }
@@ -341,7 +342,7 @@ abstract class SassNumber extends Value {
   /// appropriate value. Otherwise, this throws a [SassScriptException]. If this
   /// came from a function argument, [name] is the argument name (without the
   /// `$`). It's used for error reporting.
-  num valueInRange(num min, num max, [String? name]) {
+  double valueInRange(num min, num max, [String? name]) {
     var result = fuzzyCheckRange(value, min, max);
     if (result != null) return result;
     throw SassScriptException(
@@ -358,7 +359,7 @@ abstract class SassNumber extends Value {
   ///
   /// @nodoc
   @internal
-  num valueInRangeWithUnit(num min, num max, String name, String unit) {
+  double valueInRangeWithUnit(num min, num max, String name, String unit) {
     var result = fuzzyCheckRange(value, min, max);
     if (result != null) return result;
     throw SassScriptException(
@@ -433,7 +434,7 @@ abstract class SassNumber extends Value {
   ///
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`). It's used for error reporting.
-  num convertValue(List<String> newNumerators, List<String> newDenominators,
+  double convertValue(List<String> newNumerators, List<String> newDenominators,
           [String? name]) =>
       _coerceOrConvertValue(newNumerators, newDenominators,
           coerceUnitless: false, name: name);
@@ -465,7 +466,7 @@ abstract class SassNumber extends Value {
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`) and [otherName] is the argument name for [other]. These
   /// are used for error reporting.
-  num convertValueToMatch(SassNumber other,
+  double convertValueToMatch(SassNumber other,
           [String? name, String? otherName]) =>
       _coerceOrConvertValue(other.numeratorUnits, other.denominatorUnits,
           coerceUnitless: false,
@@ -507,13 +508,13 @@ abstract class SassNumber extends Value {
   ///
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`). It's used for error reporting.
-  num coerceValue(List<String> newNumerators, List<String> newDenominators,
+  double coerceValue(List<String> newNumerators, List<String> newDenominators,
           [String? name]) =>
       _coerceOrConvertValue(newNumerators, newDenominators,
           coerceUnitless: true, name: name);
 
   /// A shorthand for [coerceValue] with only one numerator unit.
-  num coerceValueToUnit(String unit, [String? name]) =>
+  double coerceValueToUnit(String unit, [String? name]) =>
       coerceValue([unit], [], name);
 
   /// Returns a copy of this number, converted to the same units as [other].
@@ -551,14 +552,15 @@ abstract class SassNumber extends Value {
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`) and [otherName] is the argument name for [other]. These
   /// are used for error reporting.
-  num coerceValueToMatch(SassNumber other, [String? name, String? otherName]) =>
+  double coerceValueToMatch(SassNumber other,
+          [String? name, String? otherName]) =>
       _coerceOrConvertValue(other.numeratorUnits, other.denominatorUnits,
           coerceUnitless: true, name: name, other: other, otherName: otherName);
 
   /// This has been renamed [coerceValue] for consistency with [coerceToMatch],
   /// [coerceValueToMatch], [convertToMatch], and [convertValueToMatch].
   @Deprecated("Use coerceValue instead.")
-  num valueInUnits(List<String> newNumerators, List<String> newDenominators,
+  double valueInUnits(List<String> newNumerators, List<String> newDenominators,
           [String? name]) =>
       coerceValue(newNumerators, newDenominators, name);
 
@@ -572,7 +574,7 @@ abstract class SassNumber extends Value {
   /// and [newDenominators] are derived. The [name] and [otherName] are the Sass
   /// function parameter names of [this] and [other], respectively, used for
   /// error reporting.
-  num _coerceOrConvertValue(
+  double _coerceOrConvertValue(
       List<String> newNumerators, List<String> newDenominators,
       {required bool coerceUnitless,
       String? name,
@@ -716,21 +718,6 @@ abstract class SassNumber extends Value {
     throw SassScriptException('Undefined operation "$this % $other".');
   }
 
-  /// Return [num1] modulo [num2], using Sass's modulo semantics, which it
-  /// inherited from Ruby and which differ from Dart's.
-  ///
-  /// @nodoc
-  @internal
-  num moduloLikeSass(num num1, num num2) {
-    if (num2 > 0) return num1 % num2;
-    if (num2 == 0) return double.nan;
-
-    // Dart has different mod-negative semantics than Ruby, and thus than
-    // Sass.
-    var result = num1 % num2;
-    return result == 0 ? 0 : result + num2;
-  }
-
   /// @nodoc
   @internal
   Value plus(Value other) {
@@ -784,7 +771,7 @@ abstract class SassNumber extends Value {
   ///
   /// @nodoc
   @protected
-  T _coerceUnits<T>(SassNumber other, T operation(num num1, num num2)) {
+  T _coerceUnits<T>(SassNumber other, T operation(double num1, double num2)) {
     try {
       return operation(value, other.coerceValueToMatch(this));
     } on SassScriptException {
@@ -802,8 +789,8 @@ abstract class SassNumber extends Value {
   ///
   /// @nodoc
   @protected
-  SassNumber multiplyUnits(
-      num value, List<String> otherNumerators, List<String> otherDenominators) {
+  SassNumber multiplyUnits(double value, List<String> otherNumerators,
+      List<String> otherDenominators) {
     // Short-circuit without allocating any new unit lists if possible.
     if (numeratorUnits.isEmpty) {
       if (otherDenominators.isEmpty &&
@@ -932,7 +919,7 @@ abstract class SassNumber extends Value {
   ///
   /// That is, if `X units1 == Y units2`, `X * _canonicalMultiplier(units1) == Y
   /// * _canonicalMultiplier(units2)`.
-  num _canonicalMultiplier(List<String> units) => units.fold(
+  double _canonicalMultiplier(List<String> units) => units.fold(
       1, (multiplier, unit) => multiplier * canonicalMultiplierForUnit(unit));
 
   /// Returns a multiplier that encapsulates unit equivalence with [unit].
@@ -942,7 +929,7 @@ abstract class SassNumber extends Value {
   ///
   /// @nodoc
   @protected
-  num canonicalMultiplierForUnit(String unit) {
+  double canonicalMultiplierForUnit(String unit) {
     var innerMap = _conversions[unit];
     return innerMap == null ? 1 : 1 / innerMap.values.first;
   }
diff --git a/lib/src/value/number/complex.dart b/lib/src/value/number/complex.dart
index cf82384c2..adbc362e4 100644
--- a/lib/src/value/number/complex.dart
+++ b/lib/src/value/number/complex.dart
@@ -26,10 +26,11 @@ class ComplexSassNumber extends SassNumber {
   bool get hasUnits => true;
 
   ComplexSassNumber(
-      num value, List<String> numeratorUnits, List<String> denominatorUnits)
+      double value, List<String> numeratorUnits, List<String> denominatorUnits)
       : this._(value, numeratorUnits, denominatorUnits);
 
-  ComplexSassNumber._(num value, this._numeratorUnits, this._denominatorUnits,
+  ComplexSassNumber._(
+      double value, this._numeratorUnits, this._denominatorUnits,
       [Tuple2<SassNumber, SassNumber>? asSlash])
       : super.protected(value, asSlash) {
     assert(numeratorUnits.length > 1 || denominatorUnits.isNotEmpty);
@@ -48,7 +49,7 @@ class ComplexSassNumber extends SassNumber {
   }
 
   SassNumber withValue(num value) =>
-      ComplexSassNumber._(value, numeratorUnits, denominatorUnits);
+      ComplexSassNumber._(value.toDouble(), numeratorUnits, denominatorUnits);
 
   SassNumber withSlash(SassNumber numerator, SassNumber denominator) =>
       ComplexSassNumber._(value, numeratorUnits, denominatorUnits,
diff --git a/lib/src/value/number/single_unit.dart b/lib/src/value/number/single_unit.dart
index c9e81cf7b..cb439630d 100644
--- a/lib/src/value/number/single_unit.dart
+++ b/lib/src/value/number/single_unit.dart
@@ -47,11 +47,12 @@ class SingleUnitSassNumber extends SassNumber {
 
   bool get hasUnits => true;
 
-  SingleUnitSassNumber(num value, this._unit,
+  SingleUnitSassNumber(double value, this._unit,
       [Tuple2<SassNumber, SassNumber>? asSlash])
       : super.protected(value, asSlash);
 
-  SassNumber withValue(num value) => SingleUnitSassNumber(value, _unit);
+  SassNumber withValue(num value) =>
+      SingleUnitSassNumber(value.toDouble(), _unit);
 
   SassNumber withSlash(SassNumber numerator, SassNumber denominator) =>
       SingleUnitSassNumber(value, _unit, Tuple2(numerator, denominator));
@@ -81,7 +82,8 @@ class SingleUnitSassNumber extends SassNumber {
       // Call this to generate a consistent error message.
       super.coerceToMatch(other, name, otherName);
 
-  num coerceValueToMatch(SassNumber other, [String? name, String? otherName]) =>
+  double coerceValueToMatch(SassNumber other,
+          [String? name, String? otherName]) =>
       (other is SingleUnitSassNumber
           ? _coerceValueToUnit(other._unit)
           : null) ??
@@ -94,7 +96,7 @@ class SingleUnitSassNumber extends SassNumber {
       // Call this to generate a consistent error message.
       super.convertToMatch(other, name, otherName);
 
-  num convertValueToMatch(SassNumber other,
+  double convertValueToMatch(SassNumber other,
           [String? name, String? otherName]) =>
       (other is SingleUnitSassNumber
           ? _coerceValueToUnit(other._unit)
@@ -110,7 +112,7 @@ class SingleUnitSassNumber extends SassNumber {
       // Call this to generate a consistent error message.
       super.coerce(newNumerators, newDenominators, name);
 
-  num coerceValue(List<String> newNumerators, List<String> newDenominators,
+  double coerceValue(List<String> newNumerators, List<String> newDenominators,
           [String? name]) =>
       (newNumerators.length == 1 && newDenominators.isEmpty
           ? _coerceValueToUnit(newNumerators[0])
@@ -118,7 +120,7 @@ class SingleUnitSassNumber extends SassNumber {
       // Call this to generate a consistent error message.
       super.coerceValue(newNumerators, newDenominators, name);
 
-  num coerceValueToUnit(String unit, [String? name]) =>
+  double coerceValueToUnit(String unit, [String? name]) =>
       _coerceValueToUnit(unit) ??
       // Call this to generate a consistent error message.
       super.coerceValueToUnit(unit, name);
@@ -132,7 +134,7 @@ class SingleUnitSassNumber extends SassNumber {
   }
 
   /// Like [coerceValueToUnit], except that it returns `null` if coercion fails.
-  num? _coerceValueToUnit(String unit) =>
+  double? _coerceValueToUnit(String unit) =>
       conversionFactor(unit, _unit).andThen((factor) => value * factor);
 
   SassNumber multiplyUnits(
diff --git a/lib/src/value/number/unitless.dart b/lib/src/value/number/unitless.dart
index 38116cccd..506ef6d5b 100644
--- a/lib/src/value/number/unitless.dart
+++ b/lib/src/value/number/unitless.dart
@@ -19,10 +19,10 @@ class UnitlessSassNumber extends SassNumber {
 
   bool get hasUnits => false;
 
-  UnitlessSassNumber(num value, [Tuple2<SassNumber, SassNumber>? asSlash])
+  UnitlessSassNumber(double value, [Tuple2<SassNumber, SassNumber>? asSlash])
       : super.protected(value, asSlash);
 
-  SassNumber withValue(num value) => UnitlessSassNumber(value);
+  SassNumber withValue(num value) => UnitlessSassNumber(value.toDouble());
 
   SassNumber withSlash(SassNumber numerator, SassNumber denominator) =>
       UnitlessSassNumber(value, Tuple2(numerator, denominator));
@@ -41,7 +41,8 @@ class UnitlessSassNumber extends SassNumber {
           [String? name, String? otherName]) =>
       other.withValue(value);
 
-  num coerceValueToMatch(SassNumber other, [String? name, String? otherName]) =>
+  double coerceValueToMatch(SassNumber other,
+          [String? name, String? otherName]) =>
       value;
 
   SassNumber convertToMatch(SassNumber other,
@@ -51,7 +52,7 @@ class UnitlessSassNumber extends SassNumber {
           ? super.convertToMatch(other, name, otherName)
           : this;
 
-  num convertValueToMatch(SassNumber other,
+  double convertValueToMatch(SassNumber other,
           [String? name, String? otherName]) =>
       other.hasUnits
           // Call this to generate a consistent error message.
@@ -63,11 +64,11 @@ class UnitlessSassNumber extends SassNumber {
       SassNumber.withUnits(value,
           numeratorUnits: newNumerators, denominatorUnits: newDenominators);
 
-  num coerceValue(List<String> newNumerators, List<String> newDenominators,
+  double coerceValue(List<String> newNumerators, List<String> newDenominators,
           [String? name]) =>
       value;
 
-  num coerceValueToUnit(String unit, [String? name]) => value;
+  double coerceValueToUnit(String unit, [String? name]) => value;
 
   SassBoolean greaterThan(Value other) {
     if (other is SassNumber) {
diff --git a/lib/src/visitor/serialize.dart b/lib/src/visitor/serialize.dart
index 5bae8be6e..c6c348387 100644
--- a/lib/src/visitor/serialize.dart
+++ b/lib/src/visitor/serialize.dart
@@ -776,7 +776,7 @@ class _SerializeVisitor
 
   /// Writes [number] without exponent notation and with at most
   /// [SassNumber.precision] digits after the decimal point.
-  void _writeNumber(num number) {
+  void _writeNumber(double number) {
     // Dart always converts integers to strings in the obvious way, so all we
     // have to do is clamp doubles that are close to being integers.
     var integer = fuzzyAsInt(number);
diff --git a/pkg/sass_api/CHANGELOG.md b/pkg/sass_api/CHANGELOG.md
index 7b35160c9..8ef193753 100644
--- a/pkg/sass_api/CHANGELOG.md
+++ b/pkg/sass_api/CHANGELOG.md
@@ -1,10 +1,17 @@
-## 3.1.0
+## 4.0.0
 
 ### Dart API
 
+* **Breaking change:** The first argument to `NumberExpression()` is now a
+  `double` rather than a `num`.
+
 * Add an optional `argumentName` parameter to `SassScriptException()` to make it
   easier to throw exceptions associated with particular argument names.
 
+* Most APIs that previously returned `num` now return `double`. All APIs
+  continue to _accept_ `num`, although in Dart 2.0.0 most of these APIs will be
+  changed to accept only `double`.
+
 ## 3.0.4
 
 * `UnaryOperationExpression`s with operator `not` now include a correct span,
diff --git a/pkg/sass_api/pubspec.yaml b/pkg/sass_api/pubspec.yaml
index c1f10ffa1..dd22fae72 100644
--- a/pkg/sass_api/pubspec.yaml
+++ b/pkg/sass_api/pubspec.yaml
@@ -2,7 +2,7 @@ name: sass_api
 # Note: Every time we add a new Sass AST node, we need to bump the *major*
 # version because it's a breaking change for anyone who's implementing the
 # visitor interface(s).
-version: 3.1.0-dev
+version: 4.0.0
 description: Additional APIs for Dart Sass.
 homepage: https://github.com/sass/dart-sass
 
diff --git a/test/dart_api/value/color_test.dart b/test/dart_api/value/color_test.dart
index e426bee31..bb7ee5f51 100644
--- a/test/dart_api/value/color_test.dart
+++ b/test/dart_api/value/color_test.dart
@@ -5,7 +5,6 @@
 import 'package:test/test.dart';
 
 import 'package:sass/sass.dart';
-import 'package:sass/src/util/number.dart';
 
 import 'utils.dart';
 
@@ -225,7 +224,7 @@ void main() {
 
   test("an RGBA color has an alpha channel", () {
     var color = parseValue("rgba(10, 20, 30, 0.7)") as SassColor;
-    expect(color.alpha, closeTo(0.7, epsilon));
+    expect(color.alpha, closeTo(0.7, 1e-11));
   });
 
   group("new SassColor.rgb()", () {
diff --git a/test/dart_api/value/number_test.dart b/test/dart_api/value/number_test.dart
index b2594d2a1..37f36d207 100644
--- a/test/dart_api/value/number_test.dart
+++ b/test/dart_api/value/number_test.dart
@@ -17,7 +17,7 @@ void main() {
 
     test("has the correct value", () {
       expect(value.value, equals(123));
-      expect(value.value, const TypeMatcher<int>());
+      expect(value.value, const TypeMatcher<double>());
     });
 
     test("has no units", () {