diff --git a/apiserver/src/main/java/micheal65536/vienna/apiserver/routes/SigninRouter.java b/apiserver/src/main/java/micheal65536/vienna/apiserver/routes/SigninRouter.java
index 108af78..616e6ec 100644
--- a/apiserver/src/main/java/micheal65536/vienna/apiserver/routes/SigninRouter.java
+++ b/apiserver/src/main/java/micheal65536/vienna/apiserver/routes/SigninRouter.java
@@ -31,7 +31,7 @@ record SigninRequest(String sessionTicket)
 					}
 
 					String userId = parts[0];
-					if (!userId.matches("^[0-9A-F]{16}$"))
+					if (!userId.matches("^[0-9A-F]{15,16}$"))
 					{
 						return Response.badRequest();
 					}
@@ -54,4 +54,4 @@ record SigninRequest(String sessionTicket)
 				}
 		);
 	}
-}
\ No newline at end of file
+}