diff --git a/CHANGELOG.md b/CHANGELOG.md
index c7e3a4a2a..11166ace7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,20 @@
+## 1.56.3
+
+### JavaScript API
+
+* **Potentially breaking bug fix**: Custom functions in both the modern and
+  legacy API now properly reject signatures with whitespace between the function
+  name and parentheses.
+
+* Custom functions in the legacy API now allow signatures with whitespace before
+  the function name, to match a bug in Node Sass.
+
+### Dart API
+
+* **Potentially breaking bug fix**: `Callable.fromSignature()` and
+  `AsyncCallable.fromSignature()` now reject signatures with whitespace between
+  the function name and parentheses.
+
 ## 1.56.2
 
 ### Embedded Sass
diff --git a/lib/src/node/legacy.dart b/lib/src/node/legacy.dart
index 1fe86d11f..3cda764a5 100644
--- a/lib/src/node/legacy.dart
+++ b/lib/src/node/legacy.dart
@@ -210,7 +210,7 @@ List<AsyncCallable> _parseFunctions(RenderOptions options, DateTime start,
 
     var fiber = options.fiber;
     if (fiber != null) {
-      result.add(Callable.fromSignature(signature, (arguments) {
+      result.add(Callable.fromSignature(signature.trimLeft(), (arguments) {
         var currentFiber = fiber.current;
         var jsArguments = [
           ...arguments.map(wrapValue),
@@ -230,12 +230,13 @@ List<AsyncCallable> _parseFunctions(RenderOptions options, DateTime start,
       }, requireParens: false));
     } else if (!asynch) {
       result.add(Callable.fromSignature(
-          signature,
+          signature.trimLeft(),
           (arguments) => unwrapValue((callback as JSFunction)
               .apply(context, arguments.map(wrapValue).toList())),
           requireParens: false));
     } else {
-      result.add(AsyncCallable.fromSignature(signature, (arguments) async {
+      result.add(
+          AsyncCallable.fromSignature(signature.trimLeft(), (arguments) async {
         var completer = Completer<Object?>();
         var jsArguments = [
           ...arguments.map(wrapValue),
diff --git a/lib/src/parse/stylesheet.dart b/lib/src/parse/stylesheet.dart
index ac3e9f582..ea7af982f 100644
--- a/lib/src/parse/stylesheet.dart
+++ b/lib/src/parse/stylesheet.dart
@@ -147,7 +147,6 @@ abstract class StylesheetParser extends Parser {
       {bool requireParens = true}) {
     return wrapSpanFormatException(() {
       var name = identifier();
-      whitespace();
       var arguments = requireParens || scanner.peekChar() == $lparen
           ? _argumentDeclaration()
           : ArgumentDeclaration.empty(scanner.emptySpan);
diff --git a/pubspec.yaml b/pubspec.yaml
index 36f86e43f..f4e6d8258 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: sass
-version: 1.56.2
+version: 1.56.3-dev
 description: A Sass implementation in Dart.
 homepage: https://github.com/sass/dart-sass