diff --git a/include/boost/regex/v4/cpp_regex_traits.hpp b/include/boost/regex/v4/cpp_regex_traits.hpp
index addc96cd..cd22bd8e 100644
--- a/include/boost/regex/v4/cpp_regex_traits.hpp
+++ b/include/boost/regex/v4/cpp_regex_traits.hpp
@@ -827,20 +827,20 @@ template <class charT>
 bool cpp_regex_traits_implementation<charT>::isctype(const charT c, char_class_type mask) const
 {
    return
-      ((mask & ::boost::re_detail::char_class_space) && (m_pctype->is(std::ctype<charT>::space, c)))
-      || ((mask & ::boost::re_detail::char_class_print) && (m_pctype->is(std::ctype<charT>::print, c)))
-      || ((mask & ::boost::re_detail::char_class_cntrl) && (m_pctype->is(std::ctype<charT>::cntrl, c)))
-      || ((mask & ::boost::re_detail::char_class_upper) && (m_pctype->is(std::ctype<charT>::upper, c)))
-      || ((mask & ::boost::re_detail::char_class_lower) && (m_pctype->is(std::ctype<charT>::lower, c)))
-      || ((mask & ::boost::re_detail::char_class_alpha) && (m_pctype->is(std::ctype<charT>::alpha, c)))
-      || ((mask & ::boost::re_detail::char_class_digit) && (m_pctype->is(std::ctype<charT>::digit, c)))
-      || ((mask & ::boost::re_detail::char_class_punct) && (m_pctype->is(std::ctype<charT>::punct, c)))
-      || ((mask & ::boost::re_detail::char_class_xdigit) && (m_pctype->is(std::ctype<charT>::xdigit, c)))
-      || ((mask & ::boost::re_detail::char_class_blank) && (m_pctype->is(std::ctype<charT>::space, c)) && !::boost::re_detail::is_separator(c))
+      ((mask & ::boost::re_detail::char_class_space) && (this->m_pctype->is(std::ctype<charT>::space, c)))
+      || ((mask & ::boost::re_detail::char_class_print) && (this->m_pctype->is(std::ctype<charT>::print, c)))
+      || ((mask & ::boost::re_detail::char_class_cntrl) && (this->m_pctype->is(std::ctype<charT>::cntrl, c)))
+      || ((mask & ::boost::re_detail::char_class_upper) && (this->m_pctype->is(std::ctype<charT>::upper, c)))
+      || ((mask & ::boost::re_detail::char_class_lower) && (this->m_pctype->is(std::ctype<charT>::lower, c)))
+      || ((mask & ::boost::re_detail::char_class_alpha) && (this->m_pctype->is(std::ctype<charT>::alpha, c)))
+      || ((mask & ::boost::re_detail::char_class_digit) && (this->m_pctype->is(std::ctype<charT>::digit, c)))
+      || ((mask & ::boost::re_detail::char_class_punct) && (this->m_pctype->is(std::ctype<charT>::punct, c)))
+      || ((mask & ::boost::re_detail::char_class_xdigit) && (this->m_pctype->is(std::ctype<charT>::xdigit, c)))
+      || ((mask & ::boost::re_detail::char_class_blank) && (this->m_pctype->is(std::ctype<charT>::space, c)) && !::boost::re_detail::is_separator(c))
       || ((mask & ::boost::re_detail::char_class_word) && (c == '_'))
       || ((mask & ::boost::re_detail::char_class_unicode) && ::boost::re_detail::is_extended(c))
       || ((mask & ::boost::re_detail::char_class_vertical_space) && (is_separator(c) || (c == '\v')))
-      || ((mask & ::boost::re_detail::char_class_horizontal_space) && m_pctype->is(std::ctype<charT>::space, c) && !(is_separator(c) || (c == '\v')));
+      || ((mask & ::boost::re_detail::char_class_horizontal_space) && this->m_pctype->is(std::ctype<charT>::space, c) && !(is_separator(c) || (c == '\v')));
 }
 #endif