diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index aca804280..e6ad3768f 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -53,6 +53,7 @@ class Codes(object):
     INVALID_USERNAME = "M_INVALID_USERNAME"
     SERVER_NOT_TRUSTED = "M_SERVER_NOT_TRUSTED"
     CONSENT_NOT_GIVEN = "M_CONSENT_NOT_GIVEN"
+    CANNOT_LEAVE_SERVER_NOTICE_ROOM = "M_CANNOT_LEAVE_SERVER_NOTICE_ROOM"
 
 
 class CodeMessageException(RuntimeError):
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 5263f09aa..82adfc8fd 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -306,6 +306,7 @@ class RoomMemberHandler(object):
                 raise SynapseError(
                     http_client.FORBIDDEN,
                     "You cannot leave this room",
+                    errcode=Codes.CANNOT_LEAVE_SERVER_NOTICE_ROOM,
                 )
 
         if effective_membership_state == Membership.INVITE: