1 files changed, 3 insertions, 1 deletions
diff --git a/synapse/util/caches/treecache.py b/synapse/util/caches/treecache.py
index 9a72218d85..2ea4e4e911 100644
--- a/synapse/util/caches/treecache.py
+++ b/synapse/util/caches/treecache.py
@@ -1,3 +1,5 @@
+from typing import Dict
+
 from six import itervalues
 
 SENTINEL = object()
@@ -12,7 +14,7 @@ class TreeCache(object):
 
     def __init__(self):
         self.size = 0
-        self.root = {}
+        self.root = {}  # type: Dict
 
     def __setitem__(self, key, value):
         return self.set(key, value)