18 Pa.C.S.A. §304. Ignorance or mistake.
Ignorance or mistake as to a matter of fact, for which there is reasonable explanation or excuse, is a defense if:
(1) the ignorance or mistake negatives the intent, knowledge, belief, recklessness, or negligence required to establish a material element of the offense; or
(2) the law provides that the state of mind established by such ignorance or mistake constitutes a defense.