A camshaft phaser for an internal combustion engine having—a stator (1) driven by a crankshaft of the internal combustion engine; a rotor (3) connected to the camshaft (24) for co-rotation therewith; and working chambers, which are configured between the stator (1) and the rotor (3) and which are subdivided into pressure chambers (A, B) by vanes (18) that are associated with the rotor (3); and—a pressure medium circuit having a plurality of pressure medium channels (A1, B1, C1, E1) that fulfill different functions, at least two of the pressure medium channels (A1, B1, C1, D1) merging into one another in one section (14); and one of the pressure medium channels (A1, B1, C1, D1) being separated in a pressure medium-tight manner from the other pressure medium channel (A1, B1, C1, D1) by a guide sleeve (13) that is inserted into the section (14).