diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index bebcb4af51d..2ede8d06399 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,7 @@
+2009-02-23  Rainer Orth  <ro@TechFak.Uni-Bielefeld.DE>
+
+	* s-oscons-tmplt.c [__osf__ && !_SS_MAXSIZE]: Undef AF_UNIX6.
+
 2009-02-18  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* gcc-interface/misc.c (gnat_post_options): Turn off warn_psabi.
diff --git a/gcc/ada/s-oscons-tmplt.c b/gcc/ada/s-oscons-tmplt.c
index 36a6b8eb1bc..8298f7526de 100644
--- a/gcc/ada/s-oscons-tmplt.c
+++ b/gcc/ada/s-oscons-tmplt.c
@@ -7,7 +7,7 @@
 --                                                                          --
 --                                 S p e c                                  --
 --                                                                          --
---          Copyright (C) 2000-2008, Free Software Foundation, Inc.         --
+--          Copyright (C) 2000-2009, Free Software Foundation, Inc.         --
 --                                                                          --
 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
 -- terms of the  GNU General Public License as published  by the Free Soft- --
@@ -837,6 +837,15 @@ CND(AF_INET, "IPv4 address family")
 # undef AF_INET6
 #endif
 
+/**
+ ** Tru64 UNIX V4.0F defines AF_INET6 without IPv6 support, specificially
+ ** without struct sockaddr_in6.  We use _SS_MAXSIZE (used for the definition
+ ** of struct sockaddr_storage on Tru64 UNIX V5.1) to detect this.
+ **/
+#if defined(__osf__) && !defined(_SS_MAXSIZE)
+# undef AF_INET6
+#endif
+
 #ifndef AF_INET6
 # define AF_INET6 -1
 #else