(Fstring_as_multibyte): Never return unibyte string unchanged.

Set size_byte field.

1 files changed, 6 insertions, 8 deletions

diff --git a/src/fns.c b/src/fns.c
index 6d30c09c45b..c98cb2547b8 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -871,14 +871,12 @@ If STRING is multibyte, the result is STRING itself.")
 {
   if (! STRING_MULTIBYTE (string))
     {
-      int newlen = multibyte_chars_in_text (XSTRING (string)->data,
-                                            STRING_BYTES (XSTRING (string)));
-      /* If all the chars are ASCII, STRING is already suitable.  */
-      if (newlen != STRING_BYTES (XSTRING (string)))
-        {
-          string = Fcopy_sequence (string);
-          XSTRING (string)->size = newlen;
-        }
+      int nbytes = STRING_BYTES (XSTRING (string));
+      int newlen = multibyte_chars_in_text (XSTRING (string)->data, nbytes);
+
+      string = Fcopy_sequence (string);
+      XSTRING (string)->size = newlen;
+      XSTRING (string)->size_byte = nbytes;
     }
   return string;
 }