Make no mistake about it!

make no mistake about it

What I have said or am about to say is absolutely certain; do not think otherwise. Make no mistake about it, I intend to take this all the way to the Supreme Court if I have to. Make no mistake about it, this was a carefully orchestrated crime—not some amateur job.
See also: make, mistake

Make no mistake (about it)!

sent. an expression signifying the sincerity of the speaker’s previous statements. Make no mistake! This is the real thing.
See also: make, mistake