diff --git a/usr.bin/talk/io.c b/usr.bin/talk/io.c
index 4daad7a..1fb9105 100644
--- a/usr.bin/talk/io.c
+++ b/usr.bin/talk/io.c
@@ -50,6 +50,7 @@ static const char sccsid[] = "@(#)io.c	8.1 (Berkeley) 6/6/93";
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <wctype.h>
 #define _XOPEN_SOURCE_EXTENDED
 #include <curses.h>