A computer-implemented method, computerized apparatus and computer program product for modified design debugging using differential trace back. An indication of an interface signal in a time unit in an execution resulting in a value miscompare between a design and a modification thereof is obtained. For each of the design and the modification, a data record detailing each signal value in each time unit, and a structure description detailing all components and interconnections thereamong, are obtained. A suspect root cause of the value miscompare is traced back from the interface signal in the time unit, the tracing back comprising comparing values in the data records of candidate signals selected based on the data records and the structure descriptions.