Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -407,10 +407,11 @@
 	# include <sys/types.h>
 	# include <sys/socket.h>
 	# include <netdb.h>
 	#else
 	# define _WIN32_WINNT 0x0501
+	# include <windows.h>
 	# include <ws2tcpip.h>
 	#endif
 ], [
 	struct addrinfo ai;
 	getaddrinfo(NULL, NULL, NULL, NULL);