diff --git a/lib/Makefile.m32 b/lib/Makefile.m32
index 2256f96e187438d75fa28a24228920e053785b25..a8eca47f15de38c0e2ea27a761514a7d42944621 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 fff4725c9eec86ffd2b2506fb97d8018cdb584f1..01f535fb3b4386cb0bc883d2716e99100c807511 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