diff --git a/bufferevent_sock.c b/bufferevent_sock.c
index 11dd10d3..c8fd1c7b 100644
--- a/bufferevent_sock.c
+++ b/bufferevent_sock.c
@@ -49,6 +49,7 @@
 
 #ifdef WIN32
 #include <winsock2.h>
+#include <ws2tcpip.h>
 #endif
 
 #ifdef _EVENT_HAVE_SYS_SOCKET_H