FIG. 3B shows a position of the sliding sleeve 22 in which the bevels 240, 222 of the locking element 24 and of the sliding sleeve 22 have just entered into contact with one another, but in which the locking element 24 is still latched to the mating locking element 32 of the mating plug connector 3. With reference to FIG. 2, it is clear that the elastic elements 23 are pretensioned in this position and, as a result of the displacement of the sliding sleeve 22, are compressed in a spring-elastic manner in the example shown. A further displacement of the sliding sleeve 22 causes the locking element 24 to be lifted (bent upward), as shown in particular with reference to FIG. 4B.