diff --git a/pymitter.py b/pymitter.py
index 8b85a34..52fcafd 100644
--- a/pymitter.py
+++ b/pymitter.py
@@ -199,7 +199,7 @@ def listeners_all(self):
         """
         listeners = list(self._tree[self.CB_KEY])
 
-        branches = self._tree.values()
+        branches = list(self._tree.values())
         for b in branches:
             if not isinstance(b, dict):
                 continue