A magwell extension is provided and configured to assist a user in inserting a cartridge magazine into the magwell of a firearm. The extension includes a hollow body enclosed on four sides and open at opposite ends. A coupling face defines a first of the ends and includes a pair of rails configured to engage the rim of the magwell. A stop rail extending from the coupling face lies perpendicular to the pair of rails. A locking element is configured to be coupled to the body with a portion extending from the first opening and beyond a plane defined by the coupling face. The locking element is configured to bias the rim of the magwell into secure engagement with the stop rail.