A computer program product is configured for performing a method including: receiving at least one command message specifying an I/O operation at a control unit from a channel subsystem, the at least one command message including one or more device command words (DCWs) having a data count and a suppress-length indication (SLI), the SLI configured to instruct the control unit whether to continue to perform the I/O operation in response to the control unit detecting an incorrect length condition; processing at least one of the one or more DCWs; and returning a transport response message including an incorrect length (IL) value, the IL value being a first IL value in response to the SLI being a first SLI value and the data count not matching the amount of data required, the IL value being a second IL value in response to the SLI being a second SLI value and the data count not matching the amount of data required.