diff --git a/gmachine.go b/gmachine.go
index 083b536..69b0c52 100644
--- a/gmachine.go
+++ b/gmachine.go
@@ -24,6 +24,8 @@ const (
 	OpNOOP
 	OpOUTA
 	OpINCA
+	OpINCX
+	OpINCY
 	OpDECA
 	OpDECX
 	OpDECY
@@ -68,6 +70,8 @@ var opcodes = map[string]Word{
 	"NOOP": OpNOOP,
 	"OUTA": OpOUTA,
 	"INCA": OpINCA,
+	"INCX": OpINCX,
+	"INCY": OpINCY,
 	"DECA": OpDECA,
 	"DECX": OpDECX,
 	"DECY": OpDECY,
@@ -134,6 +138,10 @@ func (g *Machine) Run() {
 			binary.Write(g.Out, binary.BigEndian, g.A)
 		case OpINCA:
 			g.A++
+		case OpINCX:
+			g.X++
+		case OpINCY:
+			g.Y++
 		case OpDECA:
 			g.A--
 		case OpDECX:
diff --git a/gmachine_test.go b/gmachine_test.go
index 6b16497..f912f2c 100644
--- a/gmachine_test.go
+++ b/gmachine_test.go
@@ -104,6 +104,32 @@ func TestINCA(t *testing.T) {
 	}
 }
 
+func TestINCX(t *testing.T) {
+	t.Parallel()
+	g := gmachine.New(nil)
+	err := assembleAndRunFromString(g, "INCX")
+	if err != nil {
+		t.Fatal("didn't expect an error:", err)
+	}
+	var wantX gmachine.Word = 1
+	if wantX != g.X {
+		t.Errorf("want X value %d, got %d", wantX, g.X)
+	}
+}
+
+func TestINCY(t *testing.T) {
+	t.Parallel()
+	g := gmachine.New(nil)
+	err := assembleAndRunFromString(g, "INCY")
+	if err != nil {
+		t.Fatal("didn't expect an error:", err)
+	}
+	var wantY gmachine.Word = 1
+	if wantY != g.Y {
+		t.Errorf("want Y value %d, got %d", wantY, g.Y)
+	}
+}
+
 func TestIllegalInstruction(t *testing.T) {
 	t.Parallel()
 	g := gmachine.New(nil)
diff --git a/testdata/gc.txtar b/testdata/gc.txtar
index e6fb34d..992755a 100644
--- a/testdata/gc.txtar
+++ b/testdata/gc.txtar
@@ -9,6 +9,6 @@ SETA 42
 OUTA
 
 -- want --
-0000000 0000 0000 0000 0b00 0000 0000 0000 2a00
+0000000 0000 0000 0000 0d00 0000 0000 0000 2a00
 0000010 0000 0000 0000 0300                    
 0000018
diff --git a/token/token.go b/token/token.go
index b773ae2..8ca1ea2 100644
--- a/token/token.go
+++ b/token/token.go
@@ -23,6 +23,8 @@ var opcodes = map[string]TokenType{
 	"NOOP": OPCODE,
 	"OUTA": OPCODE,
 	"INCA": OPCODE,
+	"INCX": OPCODE,
+	"INCY": OPCODE,
 	"DECA": OPCODE,
 	"DECX": OPCODE,
 	"DECY": OPCODE,
diff --git a/token/token_test.go b/token/token_test.go
index 4412d14..f4248cb 100644
--- a/token/token_test.go
+++ b/token/token_test.go
@@ -15,6 +15,8 @@ func TestLookupIdent(t *testing.T) {
 		{"NOOP", token.OPCODE},
 		{"OUTA", token.OPCODE},
 		{"INCA", token.OPCODE},
+		{"INCX", token.OPCODE},
+		{"INCY", token.OPCODE},
 		{"DECA", token.OPCODE},
 		{"DECX", token.OPCODE},
 		{"DECY", token.OPCODE},
@@ -29,6 +31,7 @@ func TestLookupIdent(t *testing.T) {
 		{"JUMP", token.OPCODE},
 		{"JXNZ", token.OPCODE},
 		{"X", token.REGISTER},
+		{"Y", token.REGISTER},
 		{"test", token.IDENT},
 		{".test", token.IDENT},
 	}