diff --git a/InstructionSets/M68k/Implementation/PerformImplementation.hpp b/InstructionSets/M68k/Implementation/PerformImplementation.hpp
index ea1ec6718..525135228 100644
--- a/InstructionSets/M68k/Implementation/PerformImplementation.hpp
+++ b/InstructionSets/M68k/Implementation/PerformImplementation.hpp
@@ -40,12 +40,13 @@ namespace M68k {
 
 template <
 	Model model,
-	typename FlowController
+	typename FlowController,
+	Operation operation = Operation::Undefined
 > void perform(Preinstruction instruction, CPU::SlicedInt32 &src, CPU::SlicedInt32 &dest, Status &status, FlowController &flow_controller) {
 
 #define sub_overflow() ((result ^ destination) & (destination ^ source))
 #define add_overflow() ((result ^ destination) & ~(destination ^ source))
-	switch(instruction.operation) {
+	switch((operation != Operation::Undefined) ? operation : instruction.operation) {
 		/*
 			ABCD adds the lowest bytes from the source and destination using BCD arithmetic,
 			obeying the extend flag.
diff --git a/InstructionSets/M68k/Perform.hpp b/InstructionSets/M68k/Perform.hpp
index 404ec5833..fe032ab2b 100644
--- a/InstructionSets/M68k/Perform.hpp
+++ b/InstructionSets/M68k/Perform.hpp
@@ -22,13 +22,18 @@ struct NullFlowController {
 	void consume_cycles(int)	{}
 };
 
-/// Performs @c op using @c source and @c dest (which mmay be ignored as per the semantics of the operation).
+/// Performs @c instruction using @c source and @c dest (which mmay be ignored as per the semantics of the operation).
 /// And change in processor status will be applied to @c status. If this operation raises an exception, causes a
 /// branch, or consumes additional cycles due to the particular value of the operands (on the 68000, think DIV or MUL),
 /// that'll be notified to the @c flow_controller.
+///
+/// If the template parameter @c operation is not @c Operation::Undefined then that operation will be performed, ignoring
+/// whatever is specifed in @c instruction. This allows selection either at compile time or at run time; per Godbolt all modern
+/// compilers seem to be smart enough fully to optimise the compile-time case.
 template <
 	Model model,
-	typename FlowController
+	typename FlowController,
+	Operation operation = Operation::Undefined
 > void perform(Preinstruction instruction, CPU::RegisterPair32 &source, CPU::RegisterPair32 &dest, Status &status, FlowController &flow_controller);
 
 }