diff --git a/libi2pd_client/UDPTunnel.cpp b/libi2pd_client/UDPTunnel.cpp
index dcdba14b..ba2c3275 100644
--- a/libi2pd_client/UDPTunnel.cpp
+++ b/libi2pd_client/UDPTunnel.cpp
@@ -240,6 +240,12 @@ namespace client
 	{
 		if(!ecode)
 		{
+			if (!m_UnackedDatagrams.empty () && m_NextSendPacketNum > m_UnackedDatagrams.front ().first + I2P_UDP_MAX_NUM_UNACKED_DATAGRAMS)
+			{
+				// window is full, drop packet
+				Receive ();
+				return;
+			}
 			LogPrint(eLogDebug, "UDPSession: Forward ", len, "B from ", FromEndpoint);
 			auto ts = i2p::util::GetMillisecondsSinceEpoch();
 			auto session = GetDatagramSession ();