# results that don't differ between the two trees.
 if ! test -d "$tmp/worktree"
 then
-       git worktree add --detach "$tmp/worktree" "$from" &&
+       git worktree add -f --detach "$tmp/worktree" "$from" &&
        dots=$(echo "$tmp/worktree" | sed 's#[^/]*#..#g') &&
        ln -s "$dots/config.mak" "$tmp/worktree/config.mak"
 fi