In two experiments, we explored the influence of affective state, or mood, on inadvertent plagiarism, a memory failure in which individuals either misattribute the source of an idea to themselves rather than to the true originator or simply do not recall having encountered the idea before and claim it as novel. Using a paradigm in which participants generate word puzzle solutions and later recall these solutions, we created an opportunity for participants to mistakenly claim ownership of items that were, in fact, initially generated by their computer ‘partner.’ Results of both experiments suggest that participants induced into a sad mood before solving the word puzzles made fewer source memory errors than did those induced into a happy mood. Results of Experiment 2 also imply that sad mood reduces some item memory errors. Implications for appraisal theories, such as the affect-as-information hypothesis, are discussed.