diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 19a4c14eaca1..599a3fb525ed 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,9 @@
+2015-05-31  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/66354
+	* include/bits/stl_algobase.h (__fill_a): Check length before calling
+	memset.
+
 2015-05-30  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/bits/stl_algobase.h (__equal<true>::equal): Check length
diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index 12eb7ec61f80..703e91c34e00 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -705,8 +705,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     __fill_a(_Tp* __first, _Tp* __last, const _Tp& __c)
     {
       const _Tp __tmp = __c;
-      __builtin_memset(__first, static_cast<unsigned char>(__tmp),
-		       __last - __first);
+      if (const size_t __len = __last - __first)
+	__builtin_memset(__first, static_cast<unsigned char>(__tmp), __len);
     }
 
   /**