diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index c8ff34e5f..f133458b9 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -76,6 +76,10 @@ class MessageHandler(BaseRoomHandler):
         Raises:
             SynapseError if something went wrong.
         """
+        # TODO(paul): Why does 'event' not have a 'user' object?
+        user = self.hs.parse_userid(event.user_id)
+        assert(user.is_mine)
+
         if stamp_event:
             event.content["hsob_ts"] = int(self.clock.time_msec())
 
diff --git a/tests/rest/test_rooms.py b/tests/rest/test_rooms.py
index b432cf254..cdaf948a3 100644
--- a/tests/rest/test_rooms.py
+++ b/tests/rest/test_rooms.py
@@ -51,7 +51,7 @@ class RoomPermissionsTestCase(RestTestCase):
         persistence_service.get_latest_pdus_in_context.return_value = []
 
         hs = HomeServer(
-            "test",
+            "red",
             db_pool=None,
             http_client=None,
             datastore=MemoryDataStore(),
@@ -398,7 +398,7 @@ class RoomsMemberListTestCase(RestTestCase):
         persistence_service.get_latest_pdus_in_context.return_value = []
 
         hs = HomeServer(
-            "test",
+            "red",
             db_pool=None,
             http_client=None,
             datastore=MemoryDataStore(),
@@ -476,7 +476,7 @@ class RoomsCreateTestCase(RestTestCase):
         persistence_service.get_latest_pdus_in_context.return_value = []
 
         hs = HomeServer(
-            "test",
+            "red",
             db_pool=None,
             http_client=None,
             datastore=MemoryDataStore(),
@@ -566,7 +566,7 @@ class RoomTopicTestCase(RestTestCase):
         persistence_service.get_latest_pdus_in_context.return_value = []
 
         hs = HomeServer(
-            "test",
+            "red",
             db_pool=None,
             http_client=None,
             datastore=MemoryDataStore(),
@@ -669,7 +669,7 @@ class RoomMemberStateTestCase(RestTestCase):
         persistence_service.get_latest_pdus_in_context.return_value = []
 
         hs = HomeServer(
-            "test",
+            "red",
             db_pool=None,
             http_client=None,
             datastore=MemoryDataStore(),
@@ -794,7 +794,7 @@ class RoomMessagesTestCase(RestTestCase):
         persistence_service.get_latest_pdus_in_context.return_value = []
 
         hs = HomeServer(
-            "test",
+            "red",
             db_pool=None,
             http_client=None,
             datastore=MemoryDataStore(),