Abstract: An improved progressing cavity pump of the Moineau type having a helically externally threaded rotor coacting with an internally helically threaded stator. In a Moineau pump where the pump casing is a singular tubular unit, the stator is bonded to the casing with an adhesive. When the pumps are used with a corrosive fluid, such as caustic soda, the adhesive is attacked and the stator becomes free to rotate. To prevent the stator from rotating, a rib is attached along a portion of the casing. The rib restrains the stator and prevents its rotation.