--- a/lib/sys_socket.in.h
+++ b/lib/sys_socket.in.h
@@ -44,6 +44,11 @@
 
 #@INCLUDE_NEXT@ @NEXT_SYS_SOCKET_H@
 
+#if defined _WIN32 && !defined __CYGWIN__
+# include <winsock2.h>
+# include <ws2tcpip.h>
+#endif
+
 /* The definitions of _GL_FUNCDECL_RPL etc. are copied here.  */
 
 /* The definition of _GL_ARG_NONNULL is copied here.  */