(read1): When reading from a file, default string to

multibyte only if it has some multibyte characters.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/lread.c b/src/lread.c
index 10baf509918..5fa76b08280 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2260,9 +2260,11 @@ read1 (readcharfun, pch, first_in_list)
                compiled Emacs Lisp files, and those always use the
                Emacs internal encoding.  Meanwhile, Qlambda is used
                for reading dynamic byte code (compiled with
-               byte-compile-dynamic = t).  */
+               byte-compile-dynamic = t).  So make the string multibyte
+               if the string contains any multibyte sequences.
+               (to_multibyte is a no-op if not.)  */
             to_multibyte (&p, &end, &nchars);
-            is_multibyte = 1;
+            is_multibyte = (p - read_buffer) != nchars;
           }
         else
           /* In all other cases, if we read these bytes as