diff --git a/synapse/storage/end_to_end_keys.py b/synapse/storage/end_to_end_keys.py
index 2040e022f..b9f1365f9 100644
--- a/synapse/storage/end_to_end_keys.py
+++ b/synapse/storage/end_to_end_keys.py
@@ -93,7 +93,7 @@ class EndToEndKeyStore(SQLBaseStore):
             query_clause = "user_id = ?"
             query_params.append(user_id)
 
-            if device_id:
+            if device_id is not None:
                 query_clause += " AND device_id = ?"
                 query_params.append(device_id)