diff --git a/src/network/network.cpp b/src/network/network.cpp
index 542d4f52cd..f3b036592c 100644
--- a/src/network/network.cpp
+++ b/src/network/network.cpp
@@ -422,7 +422,14 @@ static NetworkClientSocket *NetworkAllocClient(SOCKET s)
 // Close a connection
 void NetworkCloseClient(NetworkClientSocket *cs)
 {
-	assert(cs->sock != INVALID_SOCKET);
+	/*
+	 * Sending a message just before leaving the game calls cs->Send_Packets.
+	 * This might invoke this function, which means that when we close the
+	 * connection after cs->Send_Packets we will close an already closed
+	 * connection. This handles that case gracefully without having to make
+	 * that code any more complex or more aware of the validity of the socket.
+	 */
+	if (cs->sock == INVALID_SOCKET) return;
 
 	DEBUG(net, 1, "Closed client connection %d", cs->client_id);