diff --git a/lualib-src/lua-skynet.c b/lualib-src/lua-skynet.c
index 4999b5db..138234d4 100644
--- a/lualib-src/lua-skynet.c
+++ b/lualib-src/lua-skynet.c
@@ -198,6 +198,9 @@ _sendname(lua_State *L, struct skynet_context * context, const char * dest) {
 	default:
 		luaL_error(L, "skynet.send invalid param %s", lua_type(L,4));
 	}
+	if (session < 0) {
+		luaL_error(L, "skynet.send session (%d) < 0", session);
+	}
 	lua_pushinteger(L,session);
 	return 1;
 }
@@ -266,6 +269,9 @@ _send(lua_State *L) {
 	default:
 		luaL_error(L, "skynet.send invalid param %s", lua_type(L,4));
 	}
+	if (session < 0) {
+		luaL_error(L, "skynet.send session (%d) < 0", session);
+	}
 	lua_pushinteger(L,session);
 	return 1;
 }
diff --git a/lualib-src/trace_service.c b/lualib-src/trace_service.c
index acd8401f..7c3c8653 100644
--- a/lualib-src/trace_service.c
+++ b/lualib-src/trace_service.c
@@ -87,7 +87,7 @@ trace_register(struct trace_pool *p, int session) {
 		return;
 	}
 	int hash = session % HASH_SIZE;
-	assert(t->session == 0 && session !=0);
+	assert(t->session == 0 && session > 0);
 	t->session = session;
 	t->prev = NULL;
 	t->next = p->slot[hash];
@@ -114,7 +114,7 @@ trace_yield(struct trace_pool *p) {
 
 void 
 trace_switch(struct trace_pool *p, int session) {
-	assert(p->current == NULL);
+	assert(p->current == NULL && session > 0);
 	struct trace_info *t = p->slot[session % HASH_SIZE];
 	struct trace_info *prev = NULL;
 	while (t) {