diff --git a/src/api/client/room/create.rs b/src/api/client/room/create.rs
index 2bc6033c..f5f61784 100644
--- a/src/api/client/room/create.rs
+++ b/src/api/client/room/create.rs
@@ -107,7 +107,6 @@ pub(crate) async fn create_room_route(
 
 		return Err!(Request(Forbidden("Publishing rooms to the room directory is not allowed")));
 	}
-
 	let _short_id = services
 		.rooms
 		.short
@@ -615,17 +614,26 @@ fn custom_room_id_check(services: &Services, custom_room_id: &str) -> Result<Own
 				"Custom room ID contains an unexpected `:` which is not allowed.",
 			));
 		}
+	} else if custom_room_id.starts_with('!'){
+		return Err(Error::BadRequest(
+			ErrorKind::InvalidParam, 
+			"Room ID is prefixed with !, but is not fully qualified. You likely did not want this."));
 	} else {
 		room_id = format!("!{custom_room_id}:{server_name}");
 	}
-
 	OwnedRoomId::parse(room_id)
 		.map_err(Into::into)
+		.and_then(
+			|full_room_id| {
+				if full_room_id.server_name().expect("failed to extract server name from room ID") != server_name {
+					Err(Error::BadRequest(ErrorKind::InvalidParam, "Custom room ID must be on this server."))
+				} else {
+					Ok(full_room_id)
+				}
+			}
+		)
 		.inspect(|full_room_id| {
 			debug_info!(?full_room_id, "Full custom room ID");
-			if full_room_id.server_name().expect("failed to extract server name from room ID") != server_name {
-				error!("Custom room ID does not match server name");
-			}
 		})
 		.inspect_err(|e| warn!(?e, ?custom_room_id, "Failed to create room with custom room ID",))
 }