diff --git a/MC6809/inc/mc6809.h b/MC6809/inc/mc6809.h
index 197143a..969920a 100644
--- a/MC6809/inc/mc6809.h
+++ b/MC6809/inc/mc6809.h
@@ -183,6 +183,7 @@ namespace EightBit {
 		uint8_t clr();
 		void cmp(uint8_t operand, uint8_t data);
 		void cmp(register16_t operand, register16_t data);
+		uint8_t com(uint8_t operand);
 		uint8_t neg(uint8_t operand);
 
 		register16_t m_d;
diff --git a/MC6809/src/mc6809.cpp b/MC6809/src/mc6809.cpp
index f107494..5a61141 100644
--- a/MC6809/src/mc6809.cpp
+++ b/MC6809/src/mc6809.cpp
@@ -148,6 +148,13 @@ int EightBit::mc6809::executeUnprefixed(uint8_t opcode) {
 	case 0x60:	addCycles(6);	BUS().write(neg(AM_indexed_byte()));	break;		// NEG (indexed)
 	case 0x70:	addCycles(7);	BUS().write(neg(AM_extended_byte()));	break;		// NEG (extended)
 
+	// COM
+	case 0x03:	addCycles(6);	BUS().write(com(AM_direct_byte()));		break;		// COM (COM direct)
+	case 0x43:	addCycles(2);	A() = com(A());							break;		// COM (COMA inherent)
+	case 0x53:	addCycles(2);	B() = com(B());							break;		// COM (COMB inherent)
+	case 0x63:	addCycles(6);	BUS().write(com(AM_indexed_byte()));	break;		// COM (COM indexed)
+	case 0x73:	addCycles(7);	BUS().write(com(AM_extended_byte()));	break;		// COM (COM extended)
+
 	default:
 		UNREACHABLE;
 	}
@@ -434,3 +441,11 @@ void EightBit::mc6809::cmp(register16_t operand, register16_t data) {
 	const uint32_t difference = operand.word - data.word;
 	adjustSubtraction(operand.word, data.word, difference);
 }
+
+uint8_t EightBit::mc6809::com(uint8_t operand) {
+	const uint8_t result = ~operand;
+	adjustNZ(result);
+	clearFlag(CC(), VF);
+	setFlag(CC(), CF);
+	return result;
+}