diff --git a/bower.json b/bower.json
index 73e62cc..f908bc0 100644
--- a/bower.json
+++ b/bower.json
@@ -10,7 +10,7 @@
     "mutationobservers"
   ],
   "dependencies": {
-    "WeakMap": "Polymer/WeakMap#master"
+    "WeakMap": "Polymer/WeakMap#>=0.3.0 <1.0.0"
   },
   "license": "BSD",
   "private": true,
@@ -21,4 +21,4 @@
     "test",
     "tests"
   ]
-}
+}
\ No newline at end of file