diff --git a/CHANGELOG.md b/CHANGELOG.md
index 837a3a0f..0e23c0d3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,11 @@
   embedding the sources, when using the command-line interface or the legacy JS
   API.
 
+### JS API
+
+* `SassNumber.assertUnit()` and `SassNumber.assertNoUnits()` now correctly
+  return the number called on when it passes the assertion.
+
 ## 1.51.0
 
 * **Potentially breaking change**: Change the order of maps returned by
diff --git a/lib/src/node/value/number.dart b/lib/src/node/value/number.dart
index e2c33118..fcfcd0ab 100644
--- a/lib/src/node/value/number.dart
+++ b/lib/src/node/value/number.dart
@@ -38,9 +38,9 @@ final JSClass numberClass = () {
     'assertInRange': (SassNumber self, num min, num max, [String? name]) =>
         self.valueInRange(min, max, name),
     'assertNoUnits': (SassNumber self, [String? name]) =>
-        self.assertNoUnits(name),
+        self..assertNoUnits(name),
     'assertUnit': (SassNumber self, String unit, [String? name]) =>
-        self.assertUnit(unit, name),
+        self..assertUnit(unit, name),
     'hasUnit': (SassNumber self, String unit) => self.hasUnit(unit),
     'compatibleWithUnit': (SassNumber self, String unit) =>
         self.hasUnits && self.compatibleWithUnit(unit),