Prosodic structure influences the fine-grained phonetic detail of German plosives. Phonetic characteristics that also cue the phonological fortis-lenis contrast are affected in different ways. Closure durations were longer at higher prosodic boundaries. There was also more glottal vibration in lenis plosives at smaller prosodic boundaries, which can be explained as an aerodynamic consequence of shorter closure duration. Voice onset time in lenis plosives was not affected by prosody. In contrast, VOT decreased at higher boundaries for fortis plosives, as did the maximal intensity of the release. These results demonstrate that effects of prosody on different phonetic cues can go into opposite directions, but are overall constrained by the need to maintain phonological contrasts. While prosodic effects on some cues are compatible with a 'fortition' account of prosodic strengthening or with a general feature enhancement explanation, the effects on others enhance paradigmatic contrasts only within a given prosodic position.