In a camshaft adjuster for an internal combustion engine comprising a
control valve having a control piston slidably supported in a valve
housing, an operating unit for adjusting the angular position of the
camshaft relative to a crankshaft of the engine and a drive unit with an
electric motor and a transmission structure for actuating the control
piston, the transmission is non-self-locking so that backward movement of
the valve piston can be achieved by a backward force on the valve piston.