diff --git a/include/boost/program_options/detail/utf8_codecvt_facet.hpp b/include/boost/program_options/detail/utf8_codecvt_facet.hpp
index 09a6122..356a5f5 100644
--- a/include/boost/program_options/detail/utf8_codecvt_facet.hpp
+++ b/include/boost/program_options/detail/utf8_codecvt_facet.hpp
@@ -48,6 +48,8 @@
 // specialized on those types for this to work.
 
 #include <locale>
+// for mbstate_t
+#include <wchar.h>
 
 #include <boost/program_options/config.hpp>