diff --git a/src/win/winsock.h b/src/win/winsock.h
index 7ecb755b..2af95887 100644
--- a/src/win/winsock.h
+++ b/src/win/winsock.h
@@ -54,6 +54,14 @@
 # define SIO_BASE_HANDLE 0x48000022
 #endif
 
+#ifndef MCAST_JOIN_SOURCE_GROUP
+# define MCAST_JOIN_SOURCE_GROUP 45
+#endif
+
+#ifndef MCAST_LEAVE_SOURCE_GROUP
+# define MCAST_LEAVE_SOURCE_GROUP 46
+#endif
+
 /*
  * TDI defines that are only in the DDK.
  * We only need receive flags so far.