diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 50b443158..c559d03eb 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,7 @@
+2011-01-24  Corinna Vinschen  <corinna@vinschen.de>
+
+	* include/features.h (__STDC_ISO_10646__): Define.  Add comment.
+
 2011-01-21  Corinna Vinschen  <corinna@vinschen.de>
 
 	* syscalls.cc (rename): Fix permission problem with symlinks on NFS.
diff --git a/winsup/cygwin/include/features.h b/winsup/cygwin/include/features.h
index 4b0b5f945..d2ff1c41b 100644
--- a/winsup/cygwin/include/features.h
+++ b/winsup/cygwin/include/features.h
@@ -1,6 +1,6 @@
 /* features.h
 
-   Copyright 2001, 2002, 2003, 2004 Red Hat, Inc.
+   Copyright 2001, 2002, 2003, 2004, 2011 Red Hat, Inc.
 
 This file is part of Cygwin.
 
@@ -32,4 +32,9 @@ details. */
 		   includes _BSD_SOURCE, _XOPEN_SOURCE and _POSIX_SOURCE.
 */
 
+/* The value corresponds to UNICODE version 4.0, which is the version
+   supported by XP.  Newlib supports 5.2 (2011) but so far we need the
+   MS conversions for double-byte charsets. */
+#define __STDC_ISO_10646__ 200305L
+
 #endif /* _FEATURES_H */