diff --git a/include/boost/wave/util/flex_string.hpp b/include/boost/wave/util/flex_string.hpp
index 73adbde..52ced9d 100644
--- a/include/boost/wave/util/flex_string.hpp
+++ b/include/boost/wave/util/flex_string.hpp
@@ -111,6 +111,17 @@ namespace util {
 
 namespace flex_string_details
 {
+    template <class InIt, class OutIt>
+    OutIt copy_n(InIt b, 
+        typename std::iterator_traits<InIt>::difference_type n, OutIt d)
+    {
+        for (/**/; n != 0; --n, ++b, ++d)
+        {
+            *d = *b;
+        }
+        return d;
+    }
+
     template <class Pod, class T>
     inline void pod_fill(Pod* b, Pod* e, T c)
     {