diff --git a/lib/src/functions/color.dart b/lib/src/functions/color.dart
index 6f0c03a5c..583bdb194 100644
--- a/lib/src/functions/color.dart
+++ b/lib/src/functions/color.dart
@@ -220,7 +220,7 @@ final global = UnmodifiableListView([
 ]);
 
 /// The Sass color module.
-final module = BuiltInModule("color", functions: [
+final module = BuiltInModule("color", functions: <Callable>[
   // ### RGB
   _red, _green, _blue, _mix,
 
diff --git a/lib/src/functions/list.dart b/lib/src/functions/list.dart
index fb6696058..533be29ad 100644
--- a/lib/src/functions/list.dart
+++ b/lib/src/functions/list.dart
@@ -18,7 +18,7 @@ final global = UnmodifiableListView([
 ]);
 
 /// The Sass list module.
-final module = BuiltInModule("list", functions: [
+final module = BuiltInModule("list", functions: <Callable>[
   _length, _nth, _setNth, _join, _append, _zip, _index, _isBracketed, //
   _separator, _slash
 ]);
diff --git a/lib/src/functions/map.dart b/lib/src/functions/map.dart
index f07e1c3b2..232e70997 100644
--- a/lib/src/functions/map.dart
+++ b/lib/src/functions/map.dart
@@ -23,7 +23,7 @@ final global = UnmodifiableListView([
 ]);
 
 /// The Sass map module.
-final module = BuiltInModule("map", functions: [
+final module = BuiltInModule("map", functions: <Callable>[
   _get,
   _set,
   _merge,
diff --git a/lib/src/functions/math.dart b/lib/src/functions/math.dart
index d0b0f151c..d57dcf812 100644
--- a/lib/src/functions/math.dart
+++ b/lib/src/functions/math.dart
@@ -22,7 +22,7 @@ final global = UnmodifiableListView([
 ]);
 
 /// The Sass math module.
-final module = BuiltInModule("math", functions: [
+final module = BuiltInModule("math", functions: <Callable>[
   _abs, _acos, _asin, _atan, _atan2, _ceil, _clamp, _cos, _compatible, //
   _floor, _hypot, _isUnitless, _log, _max, _min, _percentage, _pow, //
   _randomFunction, _round, _sin, _sqrt, _tan, _unit, _div
diff --git a/lib/src/functions/selector.dart b/lib/src/functions/selector.dart
index 1bf2378b2..0be1fd866 100644
--- a/lib/src/functions/selector.dart
+++ b/lib/src/functions/selector.dart
@@ -27,7 +27,7 @@ final global = UnmodifiableListView([
 ]);
 
 /// The Sass selector module.
-final module = BuiltInModule("selector", functions: [
+final module = BuiltInModule("selector", functions: <Callable>[
   _isSuperselector,
   _simpleSelectors,
   _parse,
diff --git a/lib/src/functions/string.dart b/lib/src/functions/string.dart
index a6372d420..dc47a9977 100644
--- a/lib/src/functions/string.dart
+++ b/lib/src/functions/string.dart
@@ -29,7 +29,7 @@ final global = UnmodifiableListView([
 ]);
 
 /// The Sass string module.
-final module = BuiltInModule("string", functions: [
+final module = BuiltInModule("string", functions: <Callable>[
   _unquote, _quote, _toUpperCase, _toLowerCase, _length, _insert, _index, //
   _slice, _uniqueId,
 ]);