diff --git a/test/unit/behaviors.html b/test/unit/behaviors.html
index daafb592cb..27535891e3 100644
--- a/test/unit/behaviors.html
+++ b/test/unit/behaviors.html
@@ -414,11 +414,7 @@
   });
 
   test('behavior is null generates warning', function() {
-    var warned = false, oldWarn = Polymer._warn;
-    Polymer._warn = function(message) {
-      assert.match(message, /behavior is null/);
-      warned = true;
-    };
+    sinon.spy(console, 'warn');
     Polymer({
       is: 'behavior-null',
       behaviors: [
@@ -426,8 +422,8 @@
       ]
     });
     document.createElement('behavior-null');
-    assert.equal(warned, true, 'Null behaviour should generate warning');
-    Polymer.Base._warn = oldWarn;
+    assert.equal(console.warn.callCount, 1, 'Null behaviour should generate warning');
+    console.warn.restore();
   });
 
   test('behavior array is unique', function() {