diff --git a/service-src/service_snlua.c b/service-src/service_snlua.c
index 1ab533a2..89e607f6 100644
--- a/service-src/service_snlua.c
+++ b/service-src/service_snlua.c
@@ -160,5 +160,8 @@ snlua_release(struct snlua *l) {
 void
 snlua_signal(struct snlua *l, int signal) {
 	skynet_error(l->ctx, "recv a signal %d", signal);
+#ifdef lua_checksig
+	// If our lua support signal (modified lua version by skynet), trigger it.
 	skynet_sig_L = l->L;
+#endif
 }