diff --git a/service/cslave.lua b/service/cslave.lua
index fdbe9088..c380f371 100644
--- a/service/cslave.lua
+++ b/service/cslave.lua
@@ -14,7 +14,7 @@ local function read_package(fd)
 	local sz = socket.read(fd, 1)
 	assert(sz, "closed")
 	sz = string.byte(sz)
-	local content = socket.read(fd, sz)
+	local content = assert(socket.read(fd, sz), "closed")
 	return skynet.unpack(content)
 end