diff --git a/include/boost/regex/v4/w32_regex_traits.hpp b/include/boost/regex/v4/w32_regex_traits.hpp
index 0d3d6ce3..192cb535 100644
--- a/include/boost/regex/v4/w32_regex_traits.hpp
+++ b/include/boost/regex/v4/w32_regex_traits.hpp
@@ -533,8 +533,9 @@ typename w32_regex_traits_implementation<charT>::char_class_type
          return pos->second;
    }
    std::size_t id = 1 + re_detail::get_default_class_id(p1, p2);
-   BOOST_ASSERT(id < sizeof(masks) / sizeof(masks[0]));
-   return masks[id];
+   if(id < sizeof(masks) / sizeof(masks[0]))
+      return masks[id];
+   return masks[0];
 }