diff --git a/include/mcl/fp.hpp b/include/mcl/fp.hpp
index 44aab76..9fd6d74 100644
--- a/include/mcl/fp.hpp
+++ b/include/mcl/fp.hpp
@@ -120,10 +120,10 @@ public:
 		}
 		printf("\n");
 	}
-	static inline void init(bool *pb, const mpz_class& _p, fp::Mode mode = fp::FP_AUTO)
+	static inline void init(bool *pb, const mpz_class& _p, fp::Mode mode = fp::FP_AUTO, int xi_a = 0)
 	{
 		assert(maxBitSize <= MCL_MAX_BIT_SIZE);
-		*pb = op_.init(_p, maxBitSize, mode);
+		*pb = op_.init(_p, maxBitSize, xi_a, mode);
 		if (!*pb) return;
 		{ // set oneRep
 			FpT& one = *reinterpret_cast<FpT*>(op_.oneRep);
@@ -151,12 +151,12 @@ public:
 #endif
 		*pb = true;
 	}
-	static inline void init(bool *pb, const char *mstr, fp::Mode mode = fp::FP_AUTO)
+	static inline void init(bool *pb, const char *mstr, fp::Mode mode = fp::FP_AUTO, int xi_a = 0)
 	{
 		mpz_class p;
 		gmp::setStr(pb, p, mstr);
 		if (!*pb) return;
-		init(pb, p, mode);
+		init(pb, p, mode, xi_a);
 	}
 	static inline size_t getModulo(char *buf, size_t bufSize)
 	{
diff --git a/include/mcl/op.hpp b/include/mcl/op.hpp
index afbc8a4..a3b482f 100644
--- a/include/mcl/op.hpp
+++ b/include/mcl/op.hpp
@@ -341,8 +341,7 @@ struct Op {
 		*/
 		fp_mul(y, x, R2, p);
 	}
-	bool init(const mpz_class& p, size_t maxBitSize, Mode mode, size_t mclMaxBitSize = MCL_MAX_BIT_SIZE);
-	void initFp2(int xi_a);
+	bool init(const mpz_class& p, size_t maxBitSize, int xi_a, Mode mode, size_t mclMaxBitSize = MCL_MAX_BIT_SIZE);
 #ifdef MCL_USE_XBYAK
 	static FpGenerator* createFpGenerator();
 	static void destroyFpGenerator(FpGenerator *fg);
diff --git a/src/fp.cpp b/src/fp.cpp
index 473b26c..907d76d 100644
--- a/src/fp.cpp
+++ b/src/fp.cpp
@@ -362,7 +362,7 @@ static bool initForMont(Op& op, const Unit *p, Mode mode)
 	return true;
 }
 
-bool Op::init(const mpz_class& _p, size_t maxBitSize, Mode mode, size_t mclMaxBitSize)
+bool Op::init(const mpz_class& _p, size_t maxBitSize, int xi_a, Mode mode, size_t mclMaxBitSize)
 {
 	if (mclMaxBitSize != MCL_MAX_BIT_SIZE) return false;
 #ifdef MCL_USE_VINT
@@ -384,6 +384,7 @@ bool Op::init(const mpz_class& _p, size_t maxBitSize, Mode mode, size_t mclMaxBi
 	mp = _p;
 	bitSize = gmp::getBitSize(mp);
 	pmod4 = gmp::getUnit(mp, 0) % 4;
+	this->xi_a = xi_a;
 /*
 	priority : MCL_USE_XBYAK > MCL_USE_LLVM > none
 	Xbyak > llvm_mont > llvm > gmp_mont > gmp
@@ -653,10 +654,5 @@ int64_t getInt64(bool *pb, fp::Block& b, const fp::Op& op)
 	#pragma warning(pop)
 #endif
 
-void Op::initFp2(int _xi_a)
-{
-	this->xi_a = _xi_a;
-}
-
 } } // mcl::fp