return EXIT_FAILURE;
 
        if (notmuch_database_needs_upgrade (notmuch)) {
-           if (add_files_state.verbosity >= VERBOSITY_NORMAL)
+           time_t now = time (NULL);
+           struct tm *gm_time = gmtime (&now);
+
+           /* since dump files are written atomically, the amount of
+            * harm from overwriting one within a second seems
+            * relatively small. */
+
+           const char *backup_name =
+               talloc_asprintf (notmuch, "%s/dump-%04d%02d%02dT%02d%02d%02d.gz",
+                                dot_notmuch_path,
+                                gm_time->tm_year + 1900,
+                                gm_time->tm_mon + 1,
+                                gm_time->tm_mday,
+                                gm_time->tm_hour,
+                                gm_time->tm_min,
+                                gm_time->tm_sec);
+
+           if (add_files_state.verbosity >= VERBOSITY_NORMAL) {
                printf ("Welcome to a new version of notmuch! Your database will now be upgraded.\n");
+               printf ("This process is safe to interrupt.\n");
+               printf ("Backing up tags to %s...\n", backup_name);
+           }
+
+           if (notmuch_database_dump (notmuch, backup_name, "",
+                                      DUMP_FORMAT_BATCH_TAG, TRUE)) {
+               fprintf (stderr, "Backup failed. Aborting upgrade.");
+               return EXIT_FAILURE;
+           }
+
            gettimeofday (&add_files_state.tv_start, NULL);
            notmuch_database_upgrade (notmuch,
                                      add_files_state.verbosity >= VERBOSITY_NORMAL ? upgrade_print_progress : NULL,
 
 test_expect_equal "$output" ""
 
 test_begin_subtest "database upgrade from format version 1"
-output=$(notmuch new)
+output=$(notmuch new | sed -e 's/^Backing up tags to .*$/Backing up tags to FILENAME/')
 test_expect_equal "$output" "\
 Welcome to a new version of notmuch! Your database will now be upgraded.
+This process is safe to interrupt.
+Backing up tags to FILENAME
 Your notmuch database has now been upgraded to database format version 2.
 No new mail."