Prevent breaking at commas followed by tildes with `gq`

Question

When I add m to formatoptions and have nonzero textwidth, Vim will insert line breaks after commas followed by tildes when I do gq in Normal mode. In my case, Vim sometimes inserts a line break at the comma in lines like

... \dots,~$A$

converting it to

... \dots,
~$A$

when I would prefer to keep it whole, that is,

...
\dots,~$A$

instead. According to :help fo-table

letter   meaning when present in 'formatoptions'
...
m   Also break at a multibyte character above 255.  This is useful for
    Asian text where every character is a word on its own.

So this seems strange to me, since I thought both , and ~ are part of ASCII. Is there a way to prevent this behavior other than removing m?