diff --git a/libsofia-sip-ua/su/sofia-sip/su.h b/libsofia-sip-ua/su/sofia-sip/su.h
index 2b1eb660077079858461c2fe814bdd2b1cacb84c..b43bda5ae57a13ff1d9a70ae614734eb0754d539 100644
--- a/libsofia-sip-ua/su/sofia-sip/su.h
+++ b/libsofia-sip-ua/su/sofia-sip/su.h
@@ -67,11 +67,11 @@
 #  include <winsock2.h>
 #  include <ws2tcpip.h>
 #  if SU_HAVE_IN6
-#    if defined(IPPROTO_IPV6) || (_WIN32_WINNT >= 0x0600)
+#    if defined(IPPROTO_IPV6) || (_WIN32_WINNT >= 0x0501)
 /*     case 1: IPv6 defined in winsock2.h/ws2tcpip.h */
 #    else
 /*     case 2: try to use "IPv6 Tech Preview" */
-#      include <tpipv6.h>		
+#      include <tpipv6.h>
 #    endif
 #  endif
 #endif