Index: include/ctype.h
===================================================================
--- include/ctype.h	(revision 8438fb1694342537bccddf3360a1356cd891fc06)
+++ include/ctype.h	(revision 83a374d5cb96ee21969b53007029c6c2513e77d3)
@@ -41,4 +41,6 @@
 #pragma once
 
+#include "stdint.h"
+
 /* Digital Research / Alcyon C table definitions */
 
@@ -73,6 +75,6 @@
 #define	iscsymf(c)	(isalpha(c) || (((c) & 0x7f) == 0x5f))
 
-#define	toascii(c)	((c) & 0x7f)
+#define	toascii(c)	((int8_t)((c) & 0x7f))
 
-#define _toupper(c)	((c) - 'a' + 'A')
-#define _tolower(c)	((c) - 'A' + 'a')
+#define _toupper(c)	((int8_t)((c) - 'a' + 'A'))
+#define _tolower(c)	((int8_t)((c) - 'A' + 'a'))