diff --git a/src/sm_genid.c b/src/sm_genid.c
index 9a52e1d..6259b30 100644
--- a/src/sm_genid.c
+++ b/src/sm_genid.c
@@ -89,6 +89,7 @@ in this Software without prior written authorization from The Open Group.
 # else /* WIN32 */
 
 #  include <X11/Xwinsock.h>
+#  include <ws2tcpip.h>
 #  include <X11/Xw32defs.h>
 #  define X_INCLUDE_NETDB_H
 #  define XOS_USE_MTSAFE_NETDBAPI