The invention relates to a supply system for a medium, in particular for an exhaust-gas purification apparatus for the treatment of exhaust gases of an internal combustion engine, having a storage vessel for the medium, having a dosing device for dosing the medium, and having a provision line which comprises a feed line for the supply of the medium to the dosing device and a return line for returning the medium from the dosing device into the storage vessel. Flow can pass through the dosing device from a feed port to a return port of the dosing device. The provision line comprises an additional fluid connection between the feed line and the return line. The additional fluid connection opens out into the feed line upstream of the feed port of the dosing device and opens out into the return line downstream of the return port of the dosing device.