An apparatus has a processing pipeline (2) comprising an execute stage (30) and at least one front end stage (10), (20), (25) for controlling which micro operations are issued to the execute stage. The pipeline has an intra-core lockstep mode of operation in which the at least one front end stage (10), (20), (25) issues micro operations for controlling the execute stage (30) to perform main processing and checker processing. The checker processing comprises redundant operations corresponding to associated main operations of at least part of the main processing. Error handling circuitry (200), (210) is responsive to the detection of a mismatch between information associated with given checker and main operations to trigger a recovery operation to correct an error and continue forward progress of the main processing.