Index: cpptoxml/parser/rpp/pp-macro-expander.h
===================================================================
--- cpptoxml/parser/rpp/pp-macro-expander.h	(revision 1107766)
+++ cpptoxml/parser/rpp/pp-macro-expander.h	(working copy)
@@ -72,7 +72,7 @@
   int generated_lines;

 public:
-  pp_macro_expander (pp_environment &__env, pp_frame *__frame = 0):
+  explicit pp_macro_expander (pp_environment &__env, pp_frame *__frame = 0):
     env (__env), frame (__frame), lines (0), generated_lines (0) {}

   template <typename _InputIterator, typename _OutputIterator>