Cut a 6-inch length of 2-by-4 lumber. Lay the chunk of wood on a work surface with the narrow side facing up.
Draw a diagonal line on the wood from the upper left corner to the bottom right corner. Use a straight edge to create the neatest line.
Place the wood in a clamp to hold it steady. Saw along the diagonal line to create two identical triangular pieces of wood.
Smooth off all the edges and sides of the wooden wedge with sandpaper to remove any splinters and to soften any sharp corners.
Close the door with the broken lock. Place the sanded wedge on the floor in front of the door with the angle facing up and the point aimed toward the door. Kick the wedge until the point slips under the bottom of the door and the wedge is seated firmly against the face of the door.