diff --git a/boost/property_tree/detail/json_parser_read.hpp b/boost/property_tree/detail/json_parser_read.hpp
index 3849450..80d32bf 100644
--- a/boost/property_tree/detail/json_parser_read.hpp
+++ b/boost/property_tree/detail/json_parser_read.hpp
@@ -114,6 +114,7 @@ namespace boost { namespace property_tree { namespace json_parser
             a_char(context &c): c(c) { }
             void operator()(It b, It e) const
             {
+                (void)e;
                 c.string += *b;
             }
         };