A coupling, for a fluid line, having a retainer and a coupling body defining a throughbore extending from an inlet opening at a male member reception end which functionally receives a male member. The retainer has a crossbar, with two spaced retainer legs, and at least one locking arm. The retainer is mounted in a moveable manner to the coupling body in radial direction in relation to the throughbore. In a starting position when the male member is not or not fully inserted into the coupling body, one free end of a retainer leg rests upon a blocking surface on the coupling body blocking the retainer from shifting into a locking position, whereby the crossbar is in the starting position, protruding out of the coupling body. At least one free end of a retainer leg is positioned in a receptacle slot in the coupling body when the male member is functionally received into the coupling body and the retainer is shifted into a locking position, whereby the crossbar is essentially positioned in a crossbar receptacle of the coupling body in order to indicate the mounted state. The locking arm features a locking element, which in the starting position, interacts with a complementary locking element on the coupling body securing the retainer releasably within the coupling body.