diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c95a7ef05b7..dd3c6d7a2ff 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2012-01-03  Olivier Hainque  <hainque@adacore.com>
+
+	* system.h: Prior to #define, #undef fopen and freopen unconditionally.
+
 2012-01-03  Olivier Hainque  <hainque@adacore.com>
 
 	* collect2.c (main): In AIX specific computations for vector
diff --git a/gcc/system.h b/gcc/system.h
index 0a943a3a3fe..51520e19f51 100644
--- a/gcc/system.h
+++ b/gcc/system.h
@@ -47,9 +47,14 @@ along with GCC; see the file COPYING3.  If not see
 #endif
 
 /* Use the unlocked open routines from libiberty.  */
-#ifdef fopen /* fopen is a #define on VMS.  */
-#undef fopen
-#endif
+
+/* Some of these are #define on some systems, e.g. on AIX to redirect
+   the names to 64bit capable functions for LARGE_FILES support. These
+   redefs are pointless here so we can override them.  */
+
+#undef fopen 
+#undef freopen 
+
 #define fopen(PATH,MODE) fopen_unlocked(PATH,MODE)
 #define fdopen(FILDES,MODE) fdopen_unlocked(FILDES,MODE)
 #define freopen(PATH,MODE,STREAM) freopen_unlocked(PATH,MODE,STREAM)
diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index 261b8a52067..dfe18d08760 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -1,3 +1,7 @@
+2012-01-03  Olivier Hainque  <hainque@adacore.com>
+
+	* system.h: Prior to #define, #undef fopen and freopen unconditionally.
+
 2011-12-20  Joseph Myers  <joseph@codesourcery.com>
 
 	* include/cpplib.h (CLK_GNUC1X): Change to CLK_GNUC11.
diff --git a/libcpp/system.h b/libcpp/system.h
index 0f15e12737a..2a1f7096703 100644
--- a/libcpp/system.h
+++ b/libcpp/system.h
@@ -44,6 +44,14 @@ along with GCC; see the file COPYING3.  If not see
 #endif
 
 /* Use the unlocked open routines from libiberty.  */
+
+/* Some of these are #define on some systems, e.g. on AIX to redirect
+   the names to 64bit capable functions for LARGE_FILES support. These
+   redefs are pointless here so we can override them.  */
+    
+#undef fopen 
+#undef freopen 
+
 #define fopen(PATH,MODE) fopen_unlocked(PATH,MODE)
 #define fdopen(FILDES,MODE) fdopen_unlocked(FILDES,MODE)
 #define freopen(PATH,MODE,STREAM) freopen_unlocked(PATH,MODE,STREAM)