A shower door guide assembly is provided with a pair of spaced apart brackets. Each bracket has a receptacle formed therein. A crossbeam is provided with a guide formed therein for cooperation with a roller assembly of a door. The crossbeam has a cross-section sized so that terminal ends of the crossbeam are each received in one the receptacles of the pair of brackets for pivoting about a lengthwise axis of crossbeam and translation in the receptacle during installation of the crossbeam terminal ends into receptacles of the pair of brackets. The receptacles and the crossbeam are sized so that each terminal end of the crossbeam can be received in only one receptacle at only one orientation of the installed crossbeam to prevent improper installation. An alignment configuration extends from each bracket to engage a pair of wall jambs for alignment of the brackets to the wall jambs.