A method for setting indicators in a control store of a computer system for conditionally performing operations, comprises providing a control store setting instruction defining an execution condition and specifying a control store to be set according to the condition, specifying in the instruction an operand lane size over which a setting operation is to be performed, the operand lane size specified being selected from a plurality of predetermined operand lane sizes, performing the setting operation defined in the setting instruction on a per operand lane basis over a plurality of operand lanes, writing the result of the setting operation to the control store specified in the instruction to set a plurality of indicators on a lane by lane basis, wherein one or a predetermined plurality of indicators is set for each operand lane in dependence on the size of the operand lane defined in the instruction. An instruction for performing the preferred method is also disclosed.