A clamp for securing an air conditioning unit in a window without the need for any modification and/or damage to the air conditioning unit or window. The clamp includes a plurality of planar members forming two oppositely facing channels. A first channel engages the air conditioning unit rail while a second channel engages the window sash of the window. The clamp further includes two fasteners to abut the window sash and the air conditioning unit rail. The clamp therefore prevents the window from being opened and the air conditioning unit from being pushed through the window.