diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 24543a0b83cb..0aeb6c06223b 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,10 @@
+2012-06-15  Jonathan Wakely  <jwakely.gcc@gmail.com>
+
+	PR libstdc++/53578
+	* include/ext/concurrence.h (__recursive_mutex::_S_destroy): Fix
+	narrowing conversion.
+	* include/std/mutex (__recursive_mutex_base::_S_destroy): Likewise.
+
 2012-06-14  Jonathan Wakely  <jwakely.gcc@gmail.com>
 
 	PR libstdc++/53270
diff --git a/libstdc++-v3/include/ext/concurrence.h b/libstdc++-v3/include/ext/concurrence.h
index 22c433bff33c..25e218b1108b 100644
--- a/libstdc++-v3/include/ext/concurrence.h
+++ b/libstdc++-v3/include/ext/concurrence.h
@@ -284,7 +284,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     // matches a gthr-win32.h recursive mutex
     template<typename _Rm>
-      static typename __enable_if<sizeof(&_Rm::sema), void>::__type
+      static typename __enable_if<(bool)sizeof(&_Rm::sema), void>::__type
       _S_destroy(_Rm* __mx)
       {
         __gthread_mutex_t __tmp;
@@ -293,7 +293,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     // matches a recursive mutex with a member 'actual'
     template<typename _Rm>
-      static typename __enable_if<sizeof(&_Rm::actual), void>::__type
+      static typename __enable_if<(bool)sizeof(&_Rm::actual), void>::__type
       _S_destroy(_Rm* __mx)
       { __gthread_mutex_destroy(&__mx->actual); }
 
diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex
index a7ebace2c889..34d64c5b65f2 100644
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -116,13 +116,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     // matches a recursive mutex with a member 'actual'
     template<typename _Rm>
-      static typename enable_if<sizeof(&_Rm::actual), void>::type
+      static typename enable_if<(bool)sizeof(&_Rm::actual), void>::type
       _S_destroy(_Rm* __mx)
       { __gthread_mutex_destroy(&__mx->actual); }
 
     // matches a gthr-win32.h recursive mutex
     template<typename _Rm>
-      static typename enable_if<sizeof(&_Rm::sema), void>::type
+      static typename enable_if<(bool)sizeof(&_Rm::sema), void>::type
       _S_destroy(_Rm* __mx)
       {
         __gthread_mutex_t __tmp;