A system is described for providing a patch mechanism within an input/output (I/O) controller, which can be used to workaround defects and conditions existing in the I/O controller. The system includes a patch module coupled to a completion queue included in the I/O controller. The patch module is used to sample incoming cycles received by the I/O controller and to determine if the captured incoming cycle matches one or more of preprogrammed trigger conditions. The patch module is capable of working around a captured non-posted request cycle by controlling header information loaded into the completion queue and by instructing the completion queue whether or not to discard a completion received from a designated end-device.