diff --git a/src/ng/directive/ngClass.js b/src/ng/directive/ngClass.js
index 79c55d7abdd6..7794f293670a 100644
--- a/src/ng/directive/ngClass.js
+++ b/src/ng/directive/ngClass.js
@@ -26,13 +26,15 @@ function classDirective(name, selector) {
     }
 
 
-    function ngClassWatchAction(newVal, oldVal) {
+    var oldVal = undefined;
+    function ngClassWatchAction(newVal) {
       if (selector === true || scope.$index % 2 === selector) {
         if (oldVal && (newVal !== oldVal)) {
           removeClass(oldVal);
         }
         addClass(newVal);
       }
+      oldVal = newVal;
     }
 
 
diff --git a/test/ng/directive/ngClassSpec.js b/test/ng/directive/ngClassSpec.js
index 4a53030bd21f..6fcfc9f92f28 100644
--- a/test/ng/directive/ngClassSpec.js
+++ b/test/ng/directive/ngClassSpec.js
@@ -235,6 +235,15 @@ describe('ngClass', function() {
     expect(element.hasClass('too')).toBeFalsy();
   }));
 
+  it('should not mess up class application due to observing an interpolated class attribute', inject(function($rootScope, $compile) {
+    $rootScope.foo = true;
+    $rootScope.$watch("anything", function() {
+      $rootScope.foo = false;
+    });
+    element = $compile('<div ng-class="{foo:foo}"/>')($rootScope);
+    $rootScope.$digest();
+    expect(element.hasClass('foo')).toBeFalsy();
+  }));
 
   it('should update ngClassOdd/Even when model is changed by filtering', inject(function($rootScope, $compile) {
     element = $compile('<ul>' +