diff --git a/src/dns.h b/src/dns.h
index f335660..a8a03f4 100644
--- a/src/dns.h
+++ b/src/dns.h
@@ -38,6 +38,11 @@
 #if _WIN32
 #include <winsock2.h>
 #include <ws2tcpip.h>
+
+#if WINVER >= _WIN32_WINNT_VISTA
+#define AI_V4MAPPED 0x00000800
+#endif
+
 #else
 #include <sys/param.h>		/* BYTE_ORDER BIG_ENDIAN _BIG_ENDIAN */
 #include <sys/types.h>		/* socklen_t */