diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3270acbcb..90f6fd2a8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,12 @@
+## 1.66.1
+
+* Deprecate user-defined Sass functions named `round()`, `mod()`, `rem()`,
+  `sin()`, `cos()`, `tan()`, `asin()`, `acos()`, `atan()`, `atan2()`, `pow()`,
+  `sqrt()`, `hypot()`, `log()`, `exp()`, `abs()`, and `sign()`. Defining
+  functions with these names will be an error in Dart Sass 2.0.0. In a more
+  immediate release, they will also be parsed as CSS calculations in ambiguous
+  cases.
+
 ## 1.66.0
 
 * **Breaking change:** Drop support for the additional CSS calculations defined
diff --git a/lib/src/deprecation.dart b/lib/src/deprecation.dart
index 5ea363008..867f8a505 100644
--- a/lib/src/deprecation.dart
+++ b/lib/src/deprecation.dart
@@ -69,6 +69,11 @@ enum Deprecation {
       deprecatedIn: '1.62.3',
       description: 'Passing null as alpha in the ${isJS ? 'JS' : 'Dart'} API.'),
 
+  mathFunctionName('math-fn-name',
+      deprecatedIn: '1.66.1',
+      description:
+          'Defining a function with the same name as a CSS calculation.'),
+
   /// Deprecation for `@import` rules.
   import.future('import', description: '@import rules.'),
 
diff --git a/lib/src/parse/stylesheet.dart b/lib/src/parse/stylesheet.dart
index 9e9f7b2ed..cfd81fde6 100644
--- a/lib/src/parse/stylesheet.dart
+++ b/lib/src/parse/stylesheet.dart
@@ -870,6 +870,37 @@ abstract class StylesheetParser extends Parser {
             "not" ||
             "clamp") {
       error("Invalid function name.", scanner.spanFrom(start));
+    } else if (name
+        case "round" ||
+            "mod" ||
+            "rem" ||
+            "sin" ||
+            "cos" ||
+            "tan" ||
+            "asin" ||
+            "acos" ||
+            "atan" ||
+            "atan2" ||
+            "pow" ||
+            "sqrt" ||
+            "hypot" ||
+            "log" ||
+            "exp" ||
+            "abs" ||
+            "sign") {
+      var suggestion = switch (name) {
+        "sign" || "rem" || "mod" || "exp" => 'Please rename it.',
+        _ => 'Either rename it or use the math.$name() function.'
+      };
+
+      logger.warnForDeprecation(
+          Deprecation.mathFunctionName,
+          'Naming a Sass function "$name" is deprecated because it conflicts '
+          'with the new\n'
+          'CSS $name() syntax. $suggestion\n'
+          '\n'
+          'More info: https:/sass-lang.com/d/math-fn-name',
+          span: scanner.spanFrom(start));
     }
 
     whitespace();
diff --git a/pkg/sass_api/CHANGELOG.md b/pkg/sass_api/CHANGELOG.md
index bf4003b9c..1ba7b431c 100644
--- a/pkg/sass_api/CHANGELOG.md
+++ b/pkg/sass_api/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 8.2.1
+
+* No user-visible changes.
+
 ## 8.2.0
 
 * No user-visible changes.
diff --git a/pkg/sass_api/pubspec.yaml b/pkg/sass_api/pubspec.yaml
index dcf7ca03d..998025d6b 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: 8.2.0
+version: 8.2.1
 description: Additional APIs for Dart Sass.
 homepage: https://github.com/sass/dart-sass
 
@@ -10,7 +10,7 @@ environment:
   sdk: ">=3.0.0 <4.0.0"
 
 dependencies:
-  sass: 1.66.0
+  sass: 1.66.1
 
 dev_dependencies:
   dartdoc: ^5.0.0
diff --git a/pubspec.yaml b/pubspec.yaml
index 6c34677db..9ceb0d9bf 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: sass
-version: 1.66.0
+version: 1.66.1
 description: A Sass implementation in Dart.
 homepage: https://github.com/sass/dart-sass