(Fstring_as_unibyte): Set size_byte field to -1.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/fns.c b/src/fns.c
index c98cb2547b8..7bd7c5b613a 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -858,6 +858,7 @@ If STRING is unibyte, the result is STRING itself.")
     {
       string = Fcopy_sequence (string);
       XSTRING (string)->size = STRING_BYTES (XSTRING (string));
+      SET_STRING_BYTES (XSTRING (string), -1);
     }
   return string;
 }