--- ncurses-5.7/ncurses/curses.priv.h
+++ ncurses-5.7/ncurses/curses.priv.h
@@ -1452,6 +1452,8 @@ extern NCURSES_EXPORT(void) _nc_expanded
 
 /* charable.c */
 #if USE_WIDEC_SUPPORT
+#include <wchar.h>
+
 extern NCURSES_EXPORT(bool) _nc_is_charable(wchar_t);
 extern NCURSES_EXPORT(int) _nc_to_char(wint_t);
 extern NCURSES_EXPORT(wint_t) _nc_to_widechar(int);