diff --git a/bower.json b/bower.json
index 7d9e678..dde147b 100644
--- a/bower.json
+++ b/bower.json
@@ -10,8 +10,8 @@
     "shadowdom"
   ],
   "dependencies": {
-    "WeakMap": "Polymer/WeakMap#master",
-    "observe-js": "Polymer/observe-js#master"
+    "WeakMap": "Polymer/WeakMap#^0.4.0",
+    "observe-js": "Polymer/observe-js#^0.4.0"
   },
   "license": "BSD",
   "private": true,
@@ -23,4 +23,4 @@
     "test",
     "tests"
   ]
-}
+}
\ No newline at end of file