Systems and methods for identifying expressions that are potential causes of program bugs are disclosed. A program and at least one input resulting in at least one passing test of the program can be received. Further, at least one plausible repair candidate expression in the program can be identified. In addition, the methods and systems can determine whether replacement of the at least one identified expression with at least one value, which is different from a value provided by the at least one identified expression, maintains the passage of the at least one passing test. Moreover, the at least one identified expression can be output when the replacement maintains the passage of the at least one passing test to enable a determination of a modification of the program that repairs a bug in the program.