A plug with an interlock contact is disclosed. The interlock contact is arranged on a movable contact locking element of the plug. The interlock contact is arranged in an intended mating position when the contact locking element is arranged in an intended locking position. The interlock contact is arranged in the plug-in position and is pluggably aligned with a mating contact of a header matching the plug when the plug is aligned with the header, and the interlock contact electrically contacts the mating contact when the plug is plugged together with the header.