An adjustable adapter configured to position a fastening tool for driving a fastener into tongue-and-groove flooring material in order to secure the flooring material to a subfloor is disclosed. The adapter comprises a fastening tool mounting plate, a base slidably mounted to the bottom of the mounting plate and a support plate slidably mounted to the top of the mounting plate. A nose plate of the fastening tool is secured to the mounting plate between the mounting plate and the support plate and a safety actuator arm is disposed between the mounting plate and the nose plate. The base and the support plate are movable such that the adapter can be configured to engage the tongue and the top surface of various sizes and configurations of tongue-and-groove flooring materials in order to maintain a desired fastener driving angle and insertion location.