An architectural covering including a motor assembly is provided. The covering may include a head rail, an end cap enclosing an end of the head rail, a roller tube rotatably supported within the head rail at least partially by the end cap, and a motor assembly including a housing in splined engagement with the end cap to non-rotatably secure the motor assembly to the end cap. The motor assembly may be received at least partially within the roller tube and may be in driving engagement with the roller tube. A covering material may be attached to the roller tube such that rotation of the roller tube extends or retracts the covering material.