A riser lock unit is provided for quick and easy mounting onto an elevated sprinkler riser. The riser lock unit functions to retain or maintain the sprinkler riser in an elevated position, without normal spring-loaded retraction into an underlying sprinkler housing, to facilitate service and/or replacement of a sprinkler nozzle head mounted at the upper end of the riser. When desired, the riser lock unit is quickly and easily removed from the sprinkler riser.