diff --git a/a8/udpsession.cc b/a8/udpsession.cc
index 9c0d9cc..8f03157 100644
--- a/a8/udpsession.cc
+++ b/a8/udpsession.cc
@@ -14,6 +14,7 @@ namespace a8
     UdpSession::UdpSession()
     {
         max_packet_len_ = DEFAULT_MAX_PACKET_LEN;
+        SetMaxPacketLen(max_packet_len_);
     }
 
     UdpSession::~UdpSession()
@@ -33,6 +34,10 @@ namespace a8
     void UdpSession::SetMaxPacketLen(int max_packet_len)
     {
         max_packet_len_ = std::max(max_packet_len, DEFAULT_MAX_PACKET_LEN);
+        if (!recv_buff_) {
+            recv_buff_ = (char *)malloc(max_packet_len_ + 1);
+        }
+        recv_bufflen_ = 0;
     }
 
     void UdpSession::OnSocketRead(char* buf, unsigned int buflen)