diff --git a/synapse/storage/__init__.py b/synapse/storage/__init__.py
index 01c580b66..e736a857e 100644
--- a/synapse/storage/__init__.py
+++ b/synapse/storage/__init__.py
@@ -276,7 +276,7 @@ class DataStore(RoomMemberStore, RoomStore,
         def _count_r30_users(txn):
             thirty_days_in_secs = 86400 * 30
             now = int(self._clock.time_msec())
-            thirty_days_ago_in_secs = now - thirty_days_in_secs
+            thirty_days_ago_in_secs = now/1000 - thirty_days_in_secs
 
             sql = """
                 SELECT platform, COALESCE(count(*), 0) FROM (