diff --git a/lualib/skynet.lua b/lualib/skynet.lua
index 9b18467af..df3bfa2ee 100644
--- a/lualib/skynet.lua
+++ b/lualib/skynet.lua
@@ -69,6 +69,38 @@ local watching_session = {}
 local error_queue = {}
 local fork_queue = { h = 1, t = 0 }
 
+local sessionstep = 1
+local maxint32 = ((1<<31) - 1)
+
+local function check_session_wraparound(next_session)
+	sessionstep = maxint32 + 1
+	while session_id_coroutine[next_session - maxint32] do
+		next_session = c.genid() + sessionstep
+	end
+end
+
+local function auxsend(addr, id, session, msg, sz)
+	session = c.send(addr, id, session, msg, sz)
+	if not session then
+		return nil
+	end
+	local next_session = session + sessionstep
+	if next_session > maxint32 then -- wrap around
+		check_session_wraparound(next_session)
+	end
+	return session
+end
+
+local function ticommand(timeout)
+	local session = c.intcommand("TIMEOUT", timeout)
+	assert(session)
+	local next_session = session + sessionstep
+	if next_session > maxint32 then -- wrap around
+		check_session_wraparound(next_session)
+	end
+	return session
+end
+
 do ---- request/select
 	local function send_requests(self)
 		local sessions = {}
@@ -85,7 +117,7 @@ do ---- request/select
 				c.trace(tag, "call", 4)
 				c.send(addr, skynet.PTYPE_TRACE, 0, tag)
 			end
-			local session = c.send(addr, p.id , nil , p.pack(tunpack(req, 3, req.n)))
+			local session = auxsend(addr, p.id , nil , p.pack(tunpack(req, 3, req.n)))
 			if session == nil then
 				err = err or {}
 				err[#err+1] = req
@@ -188,7 +220,7 @@ do ---- request/select
 		self._error = send_requests(self)
 		self._resp = {}
 		if timeout then
-			self._timeout = c.intcommand("TIMEOUT",timeout)
+			self._timeout = ticommand(timeout)
 			session_id_coroutine[self._timeout] = self._thread
 		end
 
@@ -373,8 +405,7 @@ end
 skynet.trace_timeout(false)	-- turn off by default
 
 function skynet.timeout(ti, func)
-	local session = c.intcommand("TIMEOUT",ti)
-	assert(session)
+	local session = ticommand(ti)
 	local co = co_create_for_timeout(func, ti)
 	assert(session_id_coroutine[session] == nil)
 	session_id_coroutine[session] = co
@@ -392,8 +423,7 @@ local function suspend_sleep(session, token)
 end
 
 function skynet.sleep(ti, token)
-	local session = c.intcommand("TIMEOUT",ti)
-	assert(session)
+	local session = ticommand(ti)
 	token = token or coroutine.running()
 	local succ, ret = suspend_sleep(session, token)
 	sleep_session[token] = nil
@@ -605,7 +635,7 @@ function skynet.call(addr, typename, ...)
 	end
 
 	local p = proto[typename]
-	local session = c.send(addr, p.id , nil , p.pack(...))
+	local session = auxsend(addr, p.id , nil , p.pack(...))
 	if session == nil then
 		error("call to invalid address " .. skynet.address(addr))
 	end
@@ -619,7 +649,7 @@ function skynet.rawcall(addr, typename, msg, sz)
 		c.send(addr, skynet.PTYPE_TRACE, 0, tag)
 	end
 	local p = proto[typename]
-	local session = assert(c.send(addr, p.id , nil , msg, sz), "call to invalid address")
+	local session = assert(auxsend(addr, p.id , nil , msg, sz), "call to invalid address")
 	return yield_call(addr, session)
 end
 
@@ -627,7 +657,7 @@ function skynet.tracecall(tag, addr, typename, msg, sz)
 	c.trace(tag, "tracecall begin")
 	c.send(addr, skynet.PTYPE_TRACE, 0, tag)
 	local p = proto[typename]
-	local session = assert(c.send(addr, p.id , nil , msg, sz), "call to invalid address")
+	local session = assert(auxsend(addr, p.id , nil , msg, sz), "call to invalid address")
 	local msg, sz = yield_call(addr, session)
 	c.trace(tag, "tracecall end")
 	return msg, sz