diff --git a/gen/gen_code.cpp b/gen/gen_code.cpp
index 336330b..892fdbc 100644
--- a/gen/gen_code.cpp
+++ b/gen/gen_code.cpp
@@ -2042,6 +2042,9 @@ void put64()
 			}
 		}
 	}
+	// encodekey
+	puts("void encodekey128(const Reg32& r1, const Reg32& r2) { opEncodeKey(r1, r2, 0xFA, 0xDA); }");
+	puts("void encodekey256(const Reg32& r1, const Reg32& r2) { opEncodeKey(r1, r2, 0xFB, 0xDB); }");
 }
 
 void putAMX_TILE()
diff --git a/test/apx.cpp b/test/apx.cpp
index 0b99e20..b2675b8 100644
--- a/test/apx.cpp
+++ b/test/apx.cpp
@@ -1753,6 +1753,7 @@ CYBOZU_TEST_AUTO(kmov)
 	CYBOZU_TEST_EQUAL(c.getSize(), n);
 	CYBOZU_TEST_EQUAL_ARRAY(c.getCode(), tbl, n);
 }
+
 CYBOZU_TEST_AUTO(amx)
 {
 	struct Code : Xbyak::CodeGenerator {
@@ -1835,3 +1836,37 @@ CYBOZU_TEST_AUTO(aeskl)
 	CYBOZU_TEST_EQUAL(c.getSize(), n);
 	CYBOZU_TEST_EQUAL_ARRAY(c.getCode(), tbl, n);
 }
+
+CYBOZU_TEST_AUTO(encodekey)
+{
+	struct Code : Xbyak::CodeGenerator {
+		Code()
+		{
+			encodekey128(eax, ebx);
+			encodekey128(eax, r8d);
+			encodekey128(r8d, ebx);
+			encodekey128(r30d, r29d);
+
+			encodekey256(eax, ebx);
+			encodekey256(eax, r8d);
+			encodekey256(r8d, ebx);
+			encodekey256(r30d, r29d);
+		}
+	} c;
+	const uint8_t tbl[] = {
+		// encodekey128
+		0xf3, 0x0f, 0x38, 0xfa, 0xc3,
+		0x62, 0xd4, 0x7e, 0x08, 0xda, 0xc0,
+		0x62, 0x74, 0x7e, 0x08, 0xda, 0xc3,
+		0x62, 0x4c, 0x7e, 0x08, 0xda, 0xf5,
+		// encodekey256
+		0xf3, 0x0f, 0x38, 0xfb, 0xc3,
+		0x62, 0xd4, 0x7e, 0x08, 0xdb, 0xc0,
+		0x62, 0x74, 0x7e, 0x08, 0xdb, 0xc3,
+		0x62, 0x4c, 0x7e, 0x08, 0xdb, 0xf5,
+	};
+	const size_t n = sizeof(tbl);
+	CYBOZU_TEST_EQUAL(c.getSize(), n);
+	CYBOZU_TEST_EQUAL_ARRAY(c.getCode(), tbl, n);
+}
+
diff --git a/xbyak/xbyak.h b/xbyak/xbyak.h
index ef40b99..df00389 100644
--- a/xbyak/xbyak.h
+++ b/xbyak/xbyak.h
@@ -231,6 +231,7 @@ enum {
 	ERR_INVALID_ZU,
 	ERR_CANT_USE_REX2,
 	ERR_INVALID_DFV,
+	ERR_INVALID_REG_IDX,
 	ERR_INTERNAL // Put it at last.
 };
 
@@ -288,6 +289,7 @@ inline const char *ConvertErrorToString(int err)
 		"invalid ZU",
 		"can't use rex2",
 		"invalid dfv",
+		"invalid reg index",
 		"internal error"
 	};
 	assert(ERR_INTERNAL + 1 == sizeof(errTbl) / sizeof(*errTbl));
@@ -2738,13 +2740,21 @@ private:
 	}
 	void opAESKL(const Xmm *x, const Address& addr, uint64_t type1, uint64_t type2, uint8_t code)
 	{
-		if (x && x->getIdx() >= 16) XBYAK_THROW(ERR_BAD_COMBINATION)
+		if (x && x->getIdx() >= 16) XBYAK_THROW(ERR_INVALID_REG_IDX)
 		if (addr.hasRex2()) {
 			opROO(Reg(), addr, *x, type2, code);
 			return;
 		}
 		opRO(*x, addr, type1, code);
 	}
+	void opEncodeKey(const Reg32& r1, const Reg32& r2, uint8_t code1, uint8_t code2)
+	{
+		if (r1.getIdx() < 8 && r2.getIdx() < 8) {
+			db(0xF3); db(0x0F); db(0x38); db(code1); setModRM(3, r1.getIdx(), r2.getIdx());
+			return;
+		}
+		opROO(Reg(), r2, r1, T_MUST_EVEX|T_F3, code2);
+	}
 public:
 	unsigned int getVersion() const { return VERSION; }
 	using CodeArray::db;
diff --git a/xbyak/xbyak_mnemonic.h b/xbyak/xbyak_mnemonic.h
index a904180..b08ce7d 100644
--- a/xbyak/xbyak_mnemonic.h
+++ b/xbyak/xbyak_mnemonic.h
@@ -1934,6 +1934,8 @@ void aesenc128kl(const Xmm& x, const Address& addr) { opAESKL(&x, addr, T_F3|T_0
 void aesenc256kl(const Xmm& x, const Address& addr) { opAESKL(&x, addr, T_F3|T_0F38, T_F3|T_MUST_EVEX, 0xDE); }
 void aesencwide128kl(const Address& addr) { opAESKL(&xmm0, addr, T_F3|T_0F38, T_F3|T_MUST_EVEX, 0xD8); }
 void aesencwide256kl(const Address& addr) { opAESKL(&xmm2, addr, T_F3|T_0F38, T_F3|T_MUST_EVEX, 0xD8); }
+void encodekey128(const Reg32& r1, const Reg32& r2) { opEncodeKey(r1, r2, 0xFA, 0xDA); }
+void encodekey256(const Reg32& r1, const Reg32& r2) { opEncodeKey(r1, r2, 0xFB, 0xDB); }
 void ldtilecfg(const Address& addr) { if (opROO(Reg(), addr, tmm0, T_APX|T_0F38|T_W0, 0x49)) return; opVex(tmm0, &tmm0, addr, T_0F38|T_W0, 0x49); }
 void sttilecfg(const Address& addr) { if (opROO(Reg(), addr, tmm0, T_APX|T_66|T_0F38|T_W0, 0x49)) return; opVex(tmm0, &tmm0, addr, T_66|T_0F38 | T_W0, 0x49); }
 void tileloadd(const Tmm& tm, const Address& addr) { opAMX(tm, addr, T_F2|T_0F38|T_W0, 0x4B); }