diff --git a/lualib/skynet.lua b/lualib/skynet.lua
index 372ee8c1..366b35e4 100644
--- a/lualib/skynet.lua
+++ b/lualib/skynet.lua
@@ -178,7 +178,9 @@ end
 
 function skynet.cast(group, typename, ...)
 	local p = proto[typename]
-	return c.send(".cast", p.id, 0, mc(group, p.pack(...)))
+	if #group > 0 then
+		return c.send(".cast", p.id, 0, mc(group, p.pack(...)))
+	end
 end
 
 skynet.genid = assert(c.genid)
diff --git a/skynet-src/skynet_multicast.c b/skynet-src/skynet_multicast.c
index 12fd24a6..ba2b74bb 100644
--- a/skynet-src/skynet_multicast.c
+++ b/skynet-src/skynet_multicast.c
@@ -216,6 +216,8 @@ void
 skynet_multicast_cast(struct skynet_context * from, struct skynet_multicast_message *msg, const uint32_t *dests, int n) {
 	uint32_t source = skynet_context_handle(from);
 	skynet_multicast_copy(msg, n);
+	if (n == 0)
+		return;
 	int i;
 	int release = 0;
 	for (i=0;i<n;i++) {