Question About วันธรรมดา Pronunciation

I'm learning dates and the pronunciation of Weekday is confusing me. The romanization is wan tham-má-daa (I try not to romanize, but I had to here to make it clear), but why? วันธรรมดา has only one ม and no ร sound in sight. The two ร in the middle throw me off as well. Is this another pronunciation exception I should memorize? Thanks!