A security adapter, which is provided for connecting a first and a second fluid line portion of a fluid line. The security adapter has an inner sleeve, which at a first sleeve end region has a fastening thread provided for connection to a first fluid line portion and at a second sleeve end region has an outer thread in the form of a movement thread. The outer thread can be screwed together with an inner thread of an outer sleeve, wherein the sleeve inner circumference of the outer sleeve is provided with a stop, against which a counter stop arranged on the outer circumference of the inner sleeve bears, in a rotational end position of the security adapter such that the inner sleeve and the outer sleeve are freely rotatable in relation to one another without engagement of the inner and outer thread forming the movement thread. In a screwed-in end position, the inner sleeve is screwed by way of its outer thread into the inner thread of the outer sleeve such that a stop surface on the inner sleeve bears against a counter stop surface on the outer sleeve.