In order to prevent or minimize littering, the invention proposes a plastic closure (1) having a tamper-proof element. The plastic closure has a tamper-proof element that is as small as possible, and the plastic closure is largely secured against loss. The tamper-proof element consists of a plate (50), which is formed as part of the jacket wall (30) of the cover (3) by means of designed breaking point bridges (51, 52) and lies behind a first apron (25) in the closed state before the first opening and engages in a window (26) of the first apron by means of a locking hook. After the first opening, the plate (50) is separated from the cover and is held captive between the first apron (25) and a second, inner apron (27).