(concat): Be sure to avoid putting the same `composition'

property on the adjacent regions.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/fns.c b/src/fns.c
index fd06513a0b4..4656c41a9f3 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -830,6 +830,7 @@ concat (nargs, args, target_type, last_special)
   if (num_textprops > 0)
     {
       Lisp_Object props;
+      int last_to_end = -1;
 
       for (argnum = 0; argnum < num_textprops; argnum++)
         {
@@ -840,11 +841,11 @@ concat (nargs, args, target_type, last_special)
                                       Qnil);
           /* If successive arguments have properites, be sure that the
              value of `composition' property be the copy.  */
-          if (argnum > 0
-              && textprops[argnum - 1].argnum + 1 == textprops[argnum].argnum)
+          if (last_to_end == textprops[argnum].to)
             make_composition_value_copy (props);
           add_text_properties_from_list (val, props,
                                          make_number (textprops[argnum].to));
+          last_to_end = textprops[argnum].to + XSTRING (this)->size;
         }
     }
   return val;