diff --git a/kcp.go b/kcp.go
index 0e0a0a6..aa976bb 100644
--- a/kcp.go
+++ b/kcp.go
@@ -635,7 +635,10 @@ func (kcp *KCP) Input(data []byte, regular, ackNoDelay bool) int {
 					}
 					kcp.incr += (mss*mss)/kcp.incr + (mss / 16)
 					if (kcp.cwnd+1)*mss <= kcp.incr {
-						kcp.cwnd++
+						if mss == 0 {
+							mss = 1
+						}
+						kcp.cwnd = (kcp.incr + mss - 1) / mss
 					}
 				}
 				if kcp.cwnd > kcp.rmt_wnd {