diff --git a/InstructionSets/M50740/Executor.cpp b/InstructionSets/M50740/Executor.cpp
index c90b5afdf..5b73a939e 100644
--- a/InstructionSets/M50740/Executor.cpp
+++ b/InstructionSets/M50740/Executor.cpp
@@ -170,6 +170,10 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
 
 		case Operation::CLI:	interrupt_disable_ = 0x00;		break;
 		case Operation::SEI:	interrupt_disable_ = 0xff;		break;
+		case Operation::CLT:	index_mode_ = false;			break;
+		case Operation::SET:	index_mode_ = true;				break;
+		case Operation::CLD:	decimal_mode_ = false;			break;
+		case Operation::SED:	decimal_mode_ = true;			break;
 
 		default:
 			printf("Unimplemented operation: %d\n", int(operation));
diff --git a/InstructionSets/M50740/Executor.hpp b/InstructionSets/M50740/Executor.hpp
index 533cf7606..9f3b71fcc 100644
--- a/InstructionSets/M50740/Executor.hpp
+++ b/InstructionSets/M50740/Executor.hpp
@@ -115,6 +115,8 @@ class Executor: public CachingExecutor {
 		uint8_t negative_result_ = 0;
 		uint8_t zero_result_ = 0;
 		uint8_t interrupt_disable_ = 0;
+		bool index_mode_ = false;
+		bool decimal_mode_ = false;
 };
 
 }