diff -ruN sed-4.4/sed/mbcs.c source/sed/mbcs.c
--- sed-4.4/sed/mbcs.c	2017-01-01 03:17:10.000000000 -0800
+++ source/sed/mbcs.c	2025-06-06 04:36:30.129312397 -0700
@@ -38,6 +38,7 @@
 int
 is_mb_char (int ch, mbstate_t *cur_stat)
 {
+  return 0; // FIXME: Implement mbrtowc in relibc, then remove this line
   const char c = ch ;
   const int mb_pending = !mbsinit (cur_stat);
   const int result = mbrtowc (NULL, &c, 1, cur_stat);