A dry powder inhaler comprises at least one medicament reservoir and a closure member engaged with the reservoir so as to close an opening therein. A surface of the reservoir adjacent the opening and a surface of the closure member are in abutment, either directly or via a seal member interposed between the reservoir and the closure member. At least one abutting surface is formed with a projection that increases the contact pressure between said surfaces, thereby improving the seal between them and reducing the potential for ingress of moisture between said surfaces into the reservoir.