$NetBSD: patch-res_res__format__attr__celt.c,v 1.1 2024/04/08 03:20:09 jnemeth Exp $

--- res/res_format_attr_celt.c.orig	2022-04-14 22:16:42.000000000 +0000
+++ res/res_format_attr_celt.c
@@ -89,7 +89,7 @@ static struct ast_format *celt_parse_sdp
 
 	/* lower-case everything, so we are case-insensitive */
 	for (attrib = attribs; *attrib; ++attrib) {
-		*attrib = tolower(*attrib);
+		*attrib = tolower((unsigned char)*attrib);
 	} /* based on channels/chan_sip.c:process_a_sdp_image() */
 
 	if (sscanf(attribs, "framesize=%30u", &val) == 1) {