diff --git a/contrib/libreadline/display.c b/contrib/libreadline/display.c
index 47ff06159747..fe08861da73c 100644
--- a/contrib/libreadline/display.c
+++ b/contrib/libreadline/display.c
@@ -2380,6 +2380,8 @@ _rl_col_width (str, start, end)
 
   if (end <= start)
     return 0;
+  if (MB_CUR_MAX == 1 || rl_byte_oriented)
+    return (end - start);
 
   memset (&ps, 0, sizeof (mbstate_t));