As a software system evolves, programmers make changes that sometimes cause problems. We analyze CVS archives for fix-inducing changes—changes that lead to problems, indicated by fixes. We show how to automatically locate fix-inducing changes by linking a version archive (such as CVS) to a bug database (such as BUGZILLA). In a first investigation of the MOZILLA and ECLIPSE history, it turns out that fix-inducing changes show distinct patterns with respect to their size and the day of week they were applied. Categories and Subject Descriptors D.2.7 [Software Engineering]: Distribution, Maintenance, and Enhancement—corrections, version control; D.2.8 [Metrics]: Complexity measures General Terms Management, Measurement