diff --git a/include/ws2ipdef.h b/include/ws2ipdef.h
index e13cf6e3bbf..e4cbce1a86e 100644
--- a/include/ws2ipdef.h
+++ b/include/ws2ipdef.h
@@ -152,6 +152,12 @@ typedef struct WS(ip_mreq)
     struct WS(in_addr) imr_interface;
 } WS(IP_MREQ), *WS(PIP_MREQ);
 
+typedef struct WS(ipv6_mreq)
+{
+    struct WS(in6_addr) ipv6mr_multiaddr;
+    unsigned int ipv6mr_interface;
+} WS(IPV6_MREQ), *WS(PIPV6_MREQ);
+
 typedef struct WS(ip_mreq_source) {
     struct WS(in_addr) imr_multiaddr;
     struct WS(in_addr) imr_sourceaddr;