diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 3b44f54e91f..6f2c465a7d1 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,9 +1,17 @@
+2015-05-21  David Edelsohn  <dje.gcc@gmail.com>
+
+	PR target/66224
+	* config/cpu/powerpc/atomic_word.h (_GLIBCXX_READ_MEM_BARRIER):
+	Don't use isync. Use lwsync if available.
+	* configure.host (atomic_word_dir) [aix[56789]*]: Delete to use
+	powerpc cpu definition.
+
 2015-05-21  Jason Merrill  <jason@redhat.com>
 
 	* libsupc++/del_opv.cc: Suppress -Wsized-deallocation.
 	* libsupc++/del_op.cc: Likewise.
 
-2015-05-20  François Dumont  <fdumont@gcc.gnu.org>
+2015-05-20  François Dumont  fdumont@gcc.gnu.org>
 
 	* include/debug/formatter.h (_GLIBCXX_TYPEID): New macro to simplify
 	usage of typeid.
diff --git a/libstdc++-v3/config/cpu/powerpc/atomic_word.h b/libstdc++-v3/config/cpu/powerpc/atomic_word.h
index e044ccdddd7..1ceb02cf702 100644
--- a/libstdc++-v3/config/cpu/powerpc/atomic_word.h
+++ b/libstdc++-v3/config/cpu/powerpc/atomic_word.h
@@ -27,10 +27,11 @@
 
 typedef int _Atomic_word;
 
-#define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("isync":::"memory")
 #ifdef __NO_LWSYNC__
+#define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("sync":::"memory")
 #define _GLIBCXX_WRITE_MEM_BARRIER __asm __volatile ("sync":::"memory")
 #else
+#define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("lwsync":::"memory")
 #define _GLIBCXX_WRITE_MEM_BARRIER __asm __volatile ("lwsync":::"memory")
 #endif
 
diff --git a/libstdc++-v3/configure.host b/libstdc++-v3/configure.host
index 465a40a437e..8892f31f274 100644
--- a/libstdc++-v3/configure.host
+++ b/libstdc++-v3/configure.host
@@ -219,7 +219,6 @@ case "${host_os}" in
     # Newer versions of AIX only support PowerPC architecture, so use
     # atomic instructions directly.
     os_include_dir="os/aix"
-    atomic_word_dir="os/aix"
     ;;
   aix4.[3456789]*)
     # We set os_include_dir to os/aix only on AIX 4.3 and newer, but