diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 10a7ed4c5e2a..67b364a6c35c 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -22,7 +22,7 @@
 from twisted.internet import defer
 from twisted.internet.defer import succeed
 
-from synapse.api.constants import MAX_DEPTH, EventTypes, Membership
+from synapse.api.constants import MAX_DEPTH, EventTypes, Membership, RoomVersions
 from synapse.api.errors import (
     AuthError,
     Codes,
@@ -612,7 +612,7 @@ def handle_new_client_event(
         """
 
         if event.is_state() and (event.type, event.state_key) == (EventTypes.Create, ""):
-            room_version = event.content["room_version"]
+            room_version = event.content.get("room_version", RoomVersions.V1)
         else:
             room_version = yield self.store.get_room_version(event.room_id)