diff --git a/backbone.js b/backbone.js
index d0a1acc9..c219f516 100644
--- a/backbone.js
+++ b/backbone.js
@@ -135,7 +135,7 @@
       // Extract attributes and options.
       options || (options = {});
       if (!attrs) return this;
-      attrs = attrs.attributes || attrs;
+      if (attrs.attributes) attrs = attrs.attributes;
       var now = this.attributes;
 
       // Run validation if `validate` is defined.
diff --git a/test/speed.js b/test/speed.js
index 0f29d47f..6cd0b66c 100644
--- a/test/speed.js
+++ b/test/speed.js
@@ -22,4 +22,24 @@
     object.trigger('test:trigger2', 1, 2, 3, 4, 5);
   });
 
+  var model = new Backbone.Model;
+
+  JSLitmus.test('Model: set Math.random()', function() {
+    model.set({number: Math.random()});
+  });
+
+  var eventModel = new Backbone.Model;
+  eventModel.bind('change', fn);
+
+  JSLitmus.test('Model: set Math.random() with a change event', function() {
+    eventModel.set({number: Math.random()});
+  });
+
+  var keyModel = new Backbone.Model;
+  keyModel.bind('change:number', fn);
+
+  JSLitmus.test('Model: set Math.random() with a key-value observer', function() {
+    keyModel.set({number: Math.random()});
+  });
+
 })();
\ No newline at end of file