A packed error correction code (ECC) technique opportunistically embeds ECC check-bits with compressed data. When compressed, the data is encoded in fewer bits and is therefore fragmented when stored or transmitted compared with the uncompressed data. The ECC check-bits may be packed with compressed data at “source” points. The check-bits are transmitted along with the compressed data and, at any “intermediate” point between the source and a “destination” the check-bits may be used to detect and correct errors in the compressed data. In contrast with conventional systems, packed ECC enables end-to-end coverage for sufficiently-compressed data within the processor and also externally. While storage circuitry typically is protected by structure-specific ECC, protection is also beneficial for data as it is transmitted between processing and/or storage units.