Eli Zaretskii <eliz@gnu.org> writes:

> Here's the patch I propose to fix your variable-pitch problem:
>
> diff --git a/lisp/faces.el b/lisp/faces.el
> index c3693d1..52a4db5 100644
> --- a/lisp/faces.el
> +++ b/lisp/faces.el
> @@ -2467,7 +2467,7 @@ trailing-whitespace
>
>  ;; Definition stolen from linum.el.
>  (defface line-number
> -  '((t :inherit (shadow default)))
> +  '((t :inherit (shadow default) :family "Monospace Serif"))
>    "Face for displaying line numbers.
>  This face is used when `display-line-numbers' is non-nil.
>

This gives me a smaller line numbers by default, since I apparently have
not configured an appropriate serif font (my default font is DejaVu Sans
Mono).

What about just inheriting from fixed-pitch rather than default?