1
general::
Have no doubt, certainly, as in Make no mistake? I'll vote Republican no matter who runs. [Mid-1800s] Also see GET SOMEONE WRONG.
American Heritage Idioms
2
general::
Phrase(s): Make no mistake (about it)!
Inf. Do not be mistaken! You can be certain. • Sally: I’m very angry with you! Make no mistake about it! Fred: Whatever it’s about, I’m sorry. • Clerk: Make no mistake, this is the finest carpet available. Sally: I’d like something a little less fine, I think.
McGrawhill's American Idioms And Phrasal Verbs