f = sha1fd_check(index_name);
        } else {
                if (!index_name) {
-                       static char tmpfile[PATH_MAX];
-                       fd = odb_mkstemp(tmpfile, sizeof(tmpfile), "pack/tmp_idx_XXXXXX");
-                       index_name = xstrdup(tmpfile);
+                       static char tmp_file[PATH_MAX];
+                       fd = odb_mkstemp(tmp_file, sizeof(tmp_file), "pack/tmp_idx_XXXXXX");
+                       index_name = xstrdup(tmp_file);
                } else {
                        unlink(index_name);
                        fd = open(index_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
                }
                sha1write(f, obj->sha1, 20);
                git_SHA1_Update(&ctx, obj->sha1, 20);
+               if ((opts->flags & WRITE_IDX_STRICT) &&
+                   (i && !hashcmp(list[-2]->sha1, obj->sha1)))
+                       die("The same object %s appears twice in the pack",
+                           sha1_to_hex(obj->sha1));
        }
 
        if (index_version >= 2) {