An apparatus 2 has instruction fusing circuitry 50 for fusing two or more instructions fetched from a data store to generate a fused instruction to be processed by processing circuitry 14. A move prefix instruction is provided which indicates to the instruction fusing circuitry 50 that the move prefix instruction can be fused with an immediately following data processing instruction without needing to compare registers specified by the move prefix instruction and the immediately following instruction. This enables the instruction fusing circuitry 50 to be implemented with reduced hardware and energy cost.