A conversion operation is performed which includes a plurality of conversion actions. A conversion action includes processing an instruction to convert selected data from a source data type to a target data type. The processing includes determining whether a data type indicated using the instruction is a valid data type for a select machine. The data type is a selected data type selected from the source data type or the target data type. The selected data is converted from the source data type to the target data type, based on determining that the data type is a valid data type for the select machine. An indicator is set to a select value to indicate the data type is an invalid data type, based on determining that the data type is an invalid data type for the select machine. The indicator is checked at an end of the conversion operation.