According to an embodiment, a hearing aid comprising a custom-fit ear mold is disclosed. The custom fit ear mold includes a retention part comprising a structure adapted to lock anatomically with at least one point at a surface of the pinna and/or ear canal when the custom-fit earmold is positioned in the pinna and/or ear canal of the user. The at least one point represents at least one retention point selected from the plurality of retention possibility points (RPPs), wherein each RPP of the plurality of the RPPs comprises a point wherein a normal, at the RPP, to a tangent plane containing the RPP intersects at another point at surface of the pinna and/or ear canal such that the another point is proximal to a tympanic membrane of the user compared to position of the RPP relative to the tympanic membrane.