The UK has recently introduced regulations to prevent design features of online gambling products that may ‘encourage problem gambling behaviour’. One change has been to prohibit win-associated and celebratory audiovisual effects following monetary losses in online slots, intended to disable a misleading design feature known as ‘losses disguised as wins’ (LDWs). We assessed 26 popular online slots available to UK consumers. Contrary to regulatory guidance, 17 used win-associated sounds following LDWs, and 18 used sound effects following LDWs that we judged as ‘celebratory’. To independently validate our appraisal of these sound effects, we asked 400 UK-based gamblers to assess whether a selection of sound effects recorded from commercially available online slots communicated a positive outcome. In every case, the average consumer classifications of the recorded sounds were consistent with our own, validating our initial assessments. These results suggest that the misuse of celebratory sound effects in online slots still occurs in the UK market, despite this regulation. We argue that this is in part due to ambiguities in regulatory guidance that have enabled operators to technically comply with the regulation while circumventing its intended effect. We conclude by offering suggestions to amend and improve this regulation.