The forward had been regarded as a doubt after taking a knock to a knee in Tuesday evening’s Checkatrade Trophy victory over Peterborough.
Yet Dennis has been declared himself fit for this afternoon’s fourth round FA Cup encounter with Steve McClaren’s side.
He replaces David Wheeler, following his recall by QPR and subsequent loaning to MK Dons.
That represents one of three changes to the Blues side which lost 2-1 at Oxford United last weekend.
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Jamal Lowe is suspended and Andy Cannon cup-tied, so in come Dion Donohue and Brett Pitman.
The bench includes Academy second-year scholar Leon Maloney, who has already made his Pompey debut this season in the Checkatrade Trophy.
Pompey: MacGillivray, Walkes, Whatmough, Burgess, Brown, Naylor, Donohue, Dennis, Evans, Curtis, Pitman.
Subs: Bass, Burgess, Morris, Haunstrup, Maloney, Close, May.