An adapter for a breast shield of a breast pump for pumping human breast milk has a chamber having a first opening leading to the breast shield and a second opening remote from the breast shield. The adapter also has a flexible media separation diaphragm, which is accommodated in the chamber and separates the chamber into a pump-side and a breast-shield-side area. The chamber tapers toward the breast-shield-side opening. The chamber has the shape of a spherical dome which is cut off in the tapering area thereof. The media separation diaphragm likewise has substantially the shape of a flattened spherical dome having a flat top side, wherein the flat top side of the media separation diaphragm faces the breast-shield-side opening of the chamber. The adapter permits a minimum pressure drop over the media separation diaphragm and ensures a reliable return to the original shape of the media separation diaphragm.
