diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 25e38eebfa49..48a6a76a2d40 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2005-01-15  David Edelsohn  <edelsohn@gnu.org>
+
+	* config/rs6000/aix52.h (CPLUSPLUS_CPP_SPEC): Revert previous change.
+
 2005-01-15  John David Anglin  <dave.anglin@nrc-cnrc.gc.ca>
 
 	PR ada/19388
diff --git a/gcc/config/rs6000/aix52.h b/gcc/config/rs6000/aix52.h
index 2d9502d17dcd..887a04d35cf8 100644
--- a/gcc/config/rs6000/aix52.h
+++ b/gcc/config/rs6000/aix52.h
@@ -103,10 +103,10 @@ do {									\
   %{pthread: -D_THREAD_SAFE}"
 
 /* The GNU C++ standard library requires that these macros be 
-   defined.  */
+   defined.  Synchronize with libstdc++ os_defines.h.  */
 #undef CPLUSPLUS_CPP_SPEC                       
 #define CPLUSPLUS_CPP_SPEC			\
-  "-D_XOPEN_SOURCE=600				\
+  "-D_XOPEN_SOURCE=500				\
    -D_XOPEN_SOURCE_EXTENDED=1			\
    -D_LARGE_FILE_API				\
    -D_ALL_SOURCE				\