ARM processors are leaders in embedded systems, delivering high-performance Computing, power efficiency, and reduced cost. For this reason, there is a relevant interest for its use in the aerospace industry. This paper proposes a lockstep approach to protect against soft errors the dual-core ARM Cortex-A9 processor, which is a hard-core processor embedded into Xilinx Zynq-7000 FPGA. The lockstep is a technique based on hardware and software redundancy for error detection and correction, which uses the concepts of checkpoint combined with rollback mechanism at software level, and processor duplication and checker circuits at hardware level. The proposed approach shows that the technique can be efficiently implemented in dual-core processors to make systems more reliable in radiation environments. In terms of performance overhead, results show the dependency on the number of checkpoints with the relation between the application size and the checkpoint and rollback routines.