diff --git a/os/xdmcp.c b/os/xdmcp.c
index 7939b4138..5bdcbe9c9 100644
--- a/os/xdmcp.c
+++ b/os/xdmcp.c
@@ -1399,6 +1399,7 @@ recv_alive_msg(unsigned length)
     }
 }
 
+_X_NORETURN
 static void
 XdmcpFatal(const char *type, ARRAY8Ptr status)
 {