2 files changed, 19 insertions, 5 deletions
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index ff89259dec..e91697049c 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -328,9 +328,23 @@ class RoomKeysVersionError(SynapseError):
         self.current_version = current_version
 
 
+class UnsupportedRoomVersionError(SynapseError):
+    """The client's request to create a room used a room version that the server does
+    not support."""
+    def __init__(self):
+        super(UnsupportedRoomVersionError, self).__init__(
+            code=400,
+            msg="Homeserver does not support this room version",
+            errcode=Codes.UNSUPPORTED_ROOM_VERSION,
+        )
+
+
 class IncompatibleRoomVersionError(SynapseError):
-    """A server is trying to join a room whose version it does not support."""
+    """A server is trying to join a room whose version it does not support.
 
+    Unlike UnsupportedRoomVersionError, it is specific to the case of the make_join
+    failing.
+    """
     def __init__(self, room_version):
         super(IncompatibleRoomVersionError, self).__init__(
             code=400,
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index 485b3d0237..b2895355a8 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -77,9 +77,9 @@ class RoomVersions(object):
         EventFormatVersions.V2,
         StateResolutionVersions.V2,
     )
-    EVENTID_NOSLASH_TEST = RoomVersion(
-        "eventid-noslash-test",
-        RoomDisposition.UNSTABLE,
+    V4 = RoomVersion(
+        "4",
+        RoomDisposition.STABLE,
         EventFormatVersions.V3,
         StateResolutionVersions.V2,
     )
@@ -95,6 +95,6 @@ KNOWN_ROOM_VERSIONS = {
         RoomVersions.V2,
         RoomVersions.V3,
         RoomVersions.STATE_V2_TEST,
-        RoomVersions.EVENTID_NOSLASH_TEST,
+        RoomVersions.V4,
     )
 }   # type: dict[str, RoomVersion]