An engine includes an engine block that defines a drain-back passage and a Positive Crankcase Ventilation (PCV) passage. The drain-back passage and the PCV passage are disposed in fluid communication with each other. A cylinder head is attached to the engine block. The cylinder head defines an oil return passage. The oil return passage is disposed in fluid communication with both the drain-back passage and the PCV passage. A head gasket is disposed between the engine block and the cylinder head, and includes a shelf that extends at least partially over the PCV passage to prevent liquids draining through the oil return passage into the drain-back passage, from entering the PCV passage, while allowing gasses flowing through the oil return passage to enter the PCV passage.