diff --git a/lib/Makefile.m32 b/lib/Makefile.m32
index 2256f96e1..a8eca47f1 100644
--- a/lib/Makefile.m32
+++ b/lib/Makefile.m32
@@ -161,7 +161,7 @@ ifdef SPNEGO
   CFLAGS += -DHAVE_SPNEGO
 endif
 ifdef IPV6
-  CFLAGS += -DENABLE_IPV6
+  CFLAGS += -DENABLE_IPV6 -D_WIN32_WINNT=0x0501
 endif
 ifdef LDAPS
   CFLAGS += -DHAVE_LDAP_SSL
diff --git a/src/Makefile.m32 b/src/Makefile.m32
index fff4725c9..01f535fb3 100644
--- a/src/Makefile.m32
+++ b/src/Makefile.m32
@@ -168,7 +168,7 @@ ifdef SPNEGO
   CFLAGS += -DHAVE_SPNEGO
 endif
 ifdef IPV6
-  CFLAGS += -DENABLE_IPV6
+  CFLAGS += -DENABLE_IPV6 -D_WIN32_WINNT=0x0501
 endif
 ifdef LDAPS
   CFLAGS += -DHAVE_LDAP_SSL