An aspect includes receiving a fetch request for a data block at a cache memory system that includes cache memory that is partitioned into a plurality of cache data ways including a cache data way that contains the data block. The data block is fetched and it is determined whether the in-line ECC checking and correcting should be bypassed. The determining is based on a bypass indicator corresponding to the cache data way. Based on determining that in-line ECC checking and correcting should be bypassed, returning the fetched data block to the requestor and performing an ECC process for the fetched data block subsequent to returning the fetched data block to the requestor. Based on determining that in-line ECC checking and correcting should not be bypassed, performing the ECC process for the fetched data block and returning the fetched data block to the requestor subsequent to performing the ECC process.