diff --git a/newlib/ChangeLog b/newlib/ChangeLog
index c52f7bb0b..0bacfd7db 100644
--- a/newlib/ChangeLog
+++ b/newlib/ChangeLog
@@ -1,3 +1,8 @@
+2010-03-17  Craig Howland <howland@LGSInnovations.com>
+
+	* libc/include/sys/features.h:  Allow for _XOPEN_SOURCE to have an
+	empty definition.  Also add support for values of 500 or less.
+
 2010-03-09  Jeff Johnston  <jjohnstn@redhat.com>
 
 	* libc/posix/telldir.c (dd_loccnt): Change start index to be 1 
diff --git a/newlib/libc/include/sys/features.h b/newlib/libc/include/sys/features.h
index e7968e05a..0277fb0a5 100644
--- a/newlib/libc/include/sys/features.h
+++ b/newlib/libc/include/sys/features.h
@@ -183,13 +183,19 @@ extern "C" {
 /* Per the permission given in POSIX.1-2008 section 2.2.1, define
  * _POSIX_C_SOURCE if _XOPEN_SOURCE is defined and _POSIX_C_SOURCE is not.
  * (_XOPEN_SOURCE indicates that XSI extensions are desired by an application.)
- * This permission is first granted in 2008, but it is used for 2001, anyway.
+ * This permission is first granted in 2008, but use it for older ones, also.
+ * Allow for _XOPEN_SOURCE to be empty (from the earliest form of it, before it
+ * was required to have specific values).
  */
 #if !defined(_POSIX_C_SOURCE)  &&  defined(_XOPEN_SOURCE) 
-  #if _XOPEN_SOURCE == 700	/* POSIX.1-2008 */
+  #if (_XOPEN_SOURCE - 0) == 700	/* POSIX.1-2008 */
     #define _POSIX_C_SOURCE       200809L
-   #elif _XOPEN_SOURCE == 600	/* POSIX.1-2001 */
+   #elif (_XOPEN_SOURCE - 0) == 600	/* POSIX.1-2001 or 2004 */
     #define _POSIX_C_SOURCE       200112L
+   #elif (_XOPEN_SOURCE - 0) == 500	/* POSIX.1-1995 */
+    #define _POSIX_C_SOURCE       199506L
+   #elif (_XOPEN_SOURCE - 0) < 500	/* really old */
+    #define _POSIX_C_SOURCE       2
   #endif
 #endif