diff --git a/synapse/util/caches/treecache.py b/synapse/util/caches/treecache.py
index 1e5f87e6a..6faf2cf75 100644
--- a/synapse/util/caches/treecache.py
+++ b/synapse/util/caches/treecache.py
@@ -43,10 +43,10 @@ class TreeCache(object):
         node_and_keys.append((self.root, None))
 
         for i in range(len(node_and_keys) - 1):
-            n,k = node_and_keys[i]
+            n, k = node_and_keys[i]
 
             if n:
                 break
             node_and_keys[i+1][0].pop(k)
 
-        return popped
\ No newline at end of file
+        return popped