A spring powered roll type fiberglass window screen has side edges received in guide channels in which locking bars are pivotally and slidably received. In closing the screen, the locking bars are longitudinally slidable by a screen actuator which in turn causes the locking bars to be pivoted into engagement with the screen by action of a guide actuator tab engaging a cam surface on the locking bar. In opening the screen, the screen actuator moves the locking bar upwardly until it is pivoted out of engagement therewith by a guide cam surface on the guide channel whereupon the screen is free to move to a fully raised position, leaving behind the locking bar.