diff --git a/libs/video/targets/old_keys.c b/libs/video/targets/old_keys.c
index 8cc1cbbf4..9d872726e 100644
--- a/libs/video/targets/old_keys.c
+++ b/libs/video/targets/old_keys.c
@@ -49,6 +49,7 @@
 #include <stdlib.h>
 
 #include "QF/hash.h"
+#include "QF/qtypes.h"
 #include "QF/sys.h"
 
 #include "old_keys.h"
@@ -246,7 +247,7 @@ OK_TranslateKeyName (const char *name)
 	const char *s = name;
 	char       *d = uname;
 
-	while ((*d++ = toupper (*s)))
+	while ((*d++ = toupper ((byte) *s)))
 		s++;
 	ok = Hash_Find (old_key_table, uname);
 	if (!ok) {
diff --git a/qw/source/cl_slist.c b/qw/source/cl_slist.c
index 3e95f8684..569b711ce 100644
--- a/qw/source/cl_slist.c
+++ b/qw/source/cl_slist.c
@@ -384,9 +384,11 @@ SL_SortEntry (server_entry_t *start)
 			i = 0;
 
 			while ((start->desc[i] != '\0') && (q->desc[i] != '\0') &&
-				   (toupper (start->desc[i]) == toupper (q->desc[i])))
+				   (toupper ((byte) start->desc[i])
+					== toupper ((byte) q->desc[i])))
 				i++;
-			if (toupper (start->desc[i]) > toupper (q->desc[i])) {
+			if (toupper ((byte) start->desc[i])
+				> toupper ((byte) q->desc[i])) {
 				SL_Swap (start, q);
 				q = start;
 			}
diff --git a/qw/source/crudefile.c b/qw/source/crudefile.c
index f9c1dc427..58426ad4d 100644
--- a/qw/source/crudefile.c
+++ b/qw/source/crudefile.c
@@ -227,7 +227,7 @@ CF_Open (const char *path, const char *mode)
 
 	j = fullpath->str + strlen (fullpath->str) - strlen (path);
 	for (i = 0; path[i]; i++, j++) // strcpy, but force lowercase
-		*j = tolower (path[i]);
+		*j = tolower ((byte) path[i]);
 	*j = '\0';
 
 	if (CF_AlreadyOpen (fullpath->str, mode[0])) {
diff --git a/qw/source/sv_ccmds.c b/qw/source/sv_ccmds.c
index baf2f5c66..e52032da8 100644
--- a/qw/source/sv_ccmds.c
+++ b/qw/source/sv_ccmds.c
@@ -66,8 +66,8 @@ cvar_t     *sv_leetnickmatch;
 static qboolean
 match_char (char a, char b)
 {
-	a = tolower (sys_char_map[(byte)a]);
-	b = tolower (sys_char_map[(byte)b]);
+	a = tolower ((byte) sys_char_map[(byte) a]);
+	b = tolower ((byte) sys_char_map[(byte) b]);
 
 	if (a == b || (sv_leetnickmatch->int_val
 		&& (   (a == '1' && b == 'i') || (a == 'i' && b == '1')
diff --git a/qw/source/sv_pr_cpqw.c b/qw/source/sv_pr_cpqw.c
index 96d7b11c3..78710b4a0 100644
--- a/qw/source/sv_pr_cpqw.c
+++ b/qw/source/sv_pr_cpqw.c
@@ -256,7 +256,7 @@ KK_qwchar (char c)
 {
 	c &= 0x7f;
 	if (c >= ' ')
-		return tolower (c);
+		return tolower ((byte) c);
 	if (c >= 0x12 && c <= 0x1b)
 		return c - 0x12 + '0';
 	switch (c) {