diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index e5c4aa164..04053695d 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -865,11 +865,23 @@ class RoomCreationHandler:
         visibility = config.get("visibility", "private")
         is_public = visibility == "public"
 
-        room_id = await self._generate_and_create_room_id(
-            creator_id=user_id,
-            is_public=is_public,
-            room_version=room_version,
-        )
+        if "room_id" in config:
+            room_id = config["room_id"]
+            try:
+                await self.store.store_room(
+                    room_id=room_id,
+                    room_creator_user_id=user_id,
+                    is_public=is_public,
+                    room_version=room_version,
+                )
+            except StoreError:
+                raise SynapseError(409, "Room ID already in use", errcode="M_CONFLICT")
+        else:
+            room_id = await self._generate_and_create_room_id(
+                creator_id=user_id,
+                is_public=is_public,
+                room_version=room_version,
+            )
 
         # Check whether this visibility value is blocked by a third party module
         allowed_by_third_party_rules = (