diff --git a/include/Client.h b/include/Client.h
index 8ac7035..3c605c7 100644
--- a/include/Client.h
+++ b/include/Client.h
@@ -12,6 +12,11 @@
 
 class TServer;
 
+#ifdef WIN32
+// for socklen_t
+#include <WS2tcpip.h>
+#endif // WIN32
+
 struct TConnection final {
     SOCKET Socket;
     struct sockaddr SockAddr;