Nail-biting is currently classified as an impulse control disorder not otherwise specified. Although seldom targeted as a primary symptom, nail-biting is often associated with somatic complications and decreased quality of life. The present study assessed the effectiveness of an innovative self-help technique, titled decoupling (DC). DC aims at attenuating pathological nail-biting by performing motor sequences that decouple and rearrange the behavioral elements involved in the habit. A total of 72 participants with excessive nail-biting were recruited via specialized self-help forums and were randomized to either DC or progressive muscle relaxation (PMR) groups after baseline assessment. Four weeks later, participants underwent a similar assessment as before and were asked to rate the effectiveness of the intervention. The primary outcome parameter was the Massachusetts General Hospital Scale (MGH) adapted. Relative to the PMR group, the DC group showed significant progress in withstanding the urge to bite their nails. Furthermore, they appraised the appearance of their nails as considerably less compromised at the end of the treatment relative to participants undergoing PMR. At statistical trend level, the DC group showed a significantly greater decline on the adapted MGH relative to PMR. Despite methodological limitations, the present study asserts that the effectiveness of DC, previously shown for trichotillomania, extends to nail-biting.