diff --git a/bower.json b/bower.json
index 8bbc54a..b59f1b1 100644
--- a/bower.json
+++ b/bower.json
@@ -11,8 +11,8 @@
     "components"
   ],
   "dependencies": {
-    "MutationObservers": "Polymer/MutationObservers#master",
-    "tools": "Polymer/tools#master"
+    "MutationObservers": "Polymer/MutationObservers#>=0.4.0 <1.0.0",
+    "tools": "Polymer/tools#>=0.4.0 <1.0.0"
   },
   "license": "BSD",
   "private": true,
@@ -24,4 +24,4 @@
     "test",
     "tests"
   ]
-}
+}
\ No newline at end of file