diff --git a/lib/src/visitor/perform.dart b/lib/src/visitor/perform.dart
index 87162cb6..45e46c50 100644
--- a/lib/src/visitor/perform.dart
+++ b/lib/src/visitor/perform.dart
@@ -725,7 +725,7 @@ class _PerformVisitor
   Value visitVariableDeclaration(VariableDeclaration node) {
     if (node.isGuarded) {
       var value = _environment.getVariable(node.name);
-      if (value != null && value != sassNull) return;
+      if (value != null && value != sassNull) return null;
     }
 
     _environment.setVariable(