diff --git a/src/ng/directive/ngModel.js b/src/ng/directive/ngModel.js
index 5ed23fdec422..e6e8220d7eb0 100644
--- a/src/ng/directive/ngModel.js
+++ b/src/ng/directive/ngModel.js
@@ -1205,7 +1205,11 @@ var DEFAULT_REGEXP = /(\s+|^)default(\s+|$)/;
           var _name = 'Brian';
           $scope.user = {
             name: function(newName) {
-              return angular.isDefined(newName) ? (_name = newName) : _name;
+              // Note that newName can be undefined for two reasons:
+              // 1. Because it is called as a getter and thus called with no arguments
+              // 2. Because the property should actually be set to undefined. This happens e.g. if the
+              //    input is invalid
+              return arguments.length ? (_name = newName) : _name;
             }
           };
         }]);