The Englishman was left distraught last weekend when he failed to beat Falkirk goalkeeper Danny Rogers with a stoppage-time spot-kick.
As a result of that miss Mark Warburton’s men suffered a 2-1 defeat, allowing Championship title rivals Hibs to draw level at the table summit.
The top two now face off at Ibrox today but Miller insists his strike partner will not turn his back if Rangers are awarded another penalty.
The former Scotland striker said: “Martyn has been fine. I’m sure it’s not the first penalty he’s missed and it won’t be the last.
“I’ve watched it back and I thought it was a great save. Yeah you are expected to score penalties and with the nature of the game and the result it was a big opportunity for us.
“But I’m sure if we get another one on Monday, Waggy will step up and put it away. We’ve seen him miss chances this year but respond in the right way.
“He knows in this team other chances will come up and he will get a chance to rectify things.
“He missed the penalty against Queen of the South a few weeks back and two minutes later he popped up with the winning header.
“That’s the kind of response you are looking for - unfortunately we just didn’t have the time for that on Saturday.
“He’s got 20 goals so far this season and that’s a great return for a lad coming into a new club.”