diff --git a/changelog.d/11672.feature b/changelog.d/11672.feature
new file mode 100644
index 000000000000..ce8b3e9547f1
--- /dev/null
+++ b/changelog.d/11672.feature
@@ -0,0 +1 @@
+Return an `M_FORBIDDEN` error code instead of `M_UNKNOWN` when a spam checker module prevents a user from creating a room.
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 2bcdf32dcce1..895a1224b756 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -393,7 +393,9 @@ async def clone_existing_room(
         user_id = requester.user.to_string()
 
         if not await self.spam_checker.user_may_create_room(user_id):
-            raise SynapseError(403, "You are not permitted to create rooms")
+            raise SynapseError(
+                403, "You are not permitted to create rooms", Codes.FORBIDDEN
+            )
 
         creation_content: JsonDict = {
             "room_version": new_room_version.identifier,
@@ -685,7 +687,9 @@ async def create_room(
                 invite_3pid_list,
             )
         ):
-            raise SynapseError(403, "You are not permitted to create rooms")
+            raise SynapseError(
+                403, "You are not permitted to create rooms", Codes.FORBIDDEN
+            )
 
         if ratelimit:
             await self.request_ratelimiter.ratelimit(requester)