diff --git a/include/boost/regex/pending/unicode_iterator.hpp b/include/boost/regex/pending/unicode_iterator.hpp
index 330fd05e..14196c0a 100644
--- a/include/boost/regex/pending/unicode_iterator.hpp
+++ b/include/boost/regex/pending/unicode_iterator.hpp
@@ -69,6 +69,7 @@ Accepts UTF-32 code points and forwards them on as UTF-16 code points.
 #ifndef BOOST_NO_STD_LOCALE
 #include <sstream>
 #endif
+#include <limits.h> // CHAR_BIT
 
 namespace boost{
 
@@ -687,3 +688,4 @@ private:
 } // namespace boost
 
 #endif // BOOST_REGEX_UNICODE_ITERATOR_HPP
+