diff --git a/internal/vm/exec_funcs.go b/internal/vm/exec_funcs.go
index 55607b5..858f8bb 100644
--- a/internal/vm/exec_funcs.go
+++ b/internal/vm/exec_funcs.go
@@ -69,3 +69,13 @@ func execINX(a *Appleone, o op) error {
 	a.setNegativeIfOverflow(b)
 	return nil
 }
+
+// Y + 1 -> Y                       N Z C I D V
+//                                  + + - - - -
+func execINY(a *Appleone, o op) error {
+	b := a.cpu.y + 1
+	a.cpu.y = b
+	a.setZeroIfNeeded(b)
+	a.setNegativeIfOverflow(b)
+	return nil
+}
diff --git a/internal/vm/opcodes.go b/internal/vm/opcodes.go
index 1601278..2896aa0 100644
--- a/internal/vm/opcodes.go
+++ b/internal/vm/opcodes.go
@@ -113,13 +113,13 @@ var opcodes = map[uint8]op{
 	// addressing    assembler    opc  bytes  cyles
 	// --------------------------------------------
 	// implied       INX          E8   1      2
-	0xE8: newOp("INX", 0xE8, 1, implied, todo),
+	0xE8: newOp("INX", 0xE8, 1, implied, execINX),
 
 	// INY  Increment Index Y by One
 	// addressing    assembler    opc  bytes  cyles
 	// --------------------------------------------
 	// implied       INY          C8   1      2
-	0xC8: newOp("INY", 0xC8, 1, implied, todo),
+	0xC8: newOp("INY", 0xC8, 1, implied, execINY),
 
 	// TAX Transfer Accumulator to Index X
 	// addressing    assembler    opc  bytes  cyles