diff --git a/include/mcl/fp.hpp b/include/mcl/fp.hpp
index ffb4699..2e69729 100644
--- a/include/mcl/fp.hpp
+++ b/include/mcl/fp.hpp
@@ -302,10 +302,13 @@ public:
 		}
 		cybozu::write(pb, os, buf + sizeof(buf) - len, len);
 	}
+	/*
+		mode = Mod : set x mod p if sizeof(S) * n <= 64 else error
+	*/
 	template<class S>
-	void setArray(bool *pb, const S *x, size_t n)
+	void setArray(bool *pb, const S *x, size_t n, mcl::fp::MaskMode mode = fp::NoMask)
 	{
-		*pb = fp::copyAndMask(v_, x, sizeof(S) * n, op_, fp::NoMask);
+		*pb = fp::copyAndMask(v_, x, sizeof(S) * n, op_, mode);
 		toMont();
 	}
 	/*
diff --git a/include/mcl/op.hpp b/include/mcl/op.hpp
index 347b02f..155d168 100644
--- a/include/mcl/op.hpp
+++ b/include/mcl/op.hpp
@@ -161,7 +161,8 @@ enum PrimeMode {
 enum MaskMode {
 	NoMask = 0, // throw if greater or equal
 	SmallMask = 1, // 1-bit smaller mask if greater or equal
-	MaskAndMod = 2 // mask and substract if greater or equal
+	MaskAndMod = 2, // mask and substract if greater or equal
+	Mod = 3 // mod p
 };
 
 struct Op {
@@ -174,6 +175,7 @@ struct Op {
 	mpz_class mp;
 	uint32_t pmod4;
 	mcl::SquareRoot sq;
+	mcl::Modp modp;
 	Unit half[maxUnitSize]; // (p + 1) / 2
 	Unit oneRep[maxUnitSize]; // 1(=inv R if Montgomery)
 	/*
diff --git a/src/fp.cpp b/src/fp.cpp
index ebd9477..df72d6d 100644
--- a/src/fp.cpp
+++ b/src/fp.cpp
@@ -476,6 +476,7 @@ bool Op::init(const mpz_class& _p, size_t maxBitSize, int _xi_a, Mode mode, size
 		sq.set(&b, mp);
 		if (!b) return false;
 	}
+	modp.init(mp);
 	return fp::initForMont(*this, p, mode);
 }
 
@@ -528,6 +529,27 @@ int detectIoMode(int ioMode, const std::ios_base& ios)
 bool copyAndMask(Unit *y, const void *x, size_t xByteSize, const Op& op, MaskMode maskMode)
 {
 	const size_t fpByteSize = sizeof(Unit) * op.N;
+	if (maskMode == Mod) {
+		if (xByteSize > fpByteSize * 2) return false;
+		mpz_class mx;
+		bool b;
+		gmp::setArray(&b, mx, (const char*)x, xByteSize);
+		if (!b) return false;
+#ifdef MCL_USE_VINT
+		op.modp.modp(mx, mx);
+#else
+		mx %= op.mp;
+#endif
+		const Unit *pmx = gmp::getUnit(mx);
+		size_t i = 0;
+		for (const size_t n = gmp::getUnitSize(mx); i < n; i++) {
+			y[i] = pmx[i];
+		}
+		for (; i < op.N; i++) {
+			y[i] = 0;
+		}
+		return true;
+	}
 	if (xByteSize > fpByteSize) {
 		if (maskMode == NoMask) return false;
 		xByteSize = fpByteSize;
diff --git a/test/fp_test.cpp b/test/fp_test.cpp
index 26f97b1..7e78773 100644
--- a/test/fp_test.cpp
+++ b/test/fp_test.cpp
@@ -565,6 +565,43 @@ void setArrayMaskTest2(mcl::fp::Mode mode)
 	}
 }
 
+void setArrayModTest()
+{
+	const mpz_class& p = Fp::getOp().mp;
+	const mpz_class tbl[] = {
+		0,
+		1,
+		p - 1,
+		p,
+		p + 1,
+		p * 2 - 1,
+		p * 2,
+		p * 2 + 1,
+		p * (p - 1) - 1,
+		p * (p - 1),
+		p * (p - 1) + 1,
+		p * p - 1,
+		p * p,
+		p * p + 1,
+		(mpz_class(1) << Fp::getOp().N * mcl::fp::UnitBitSize * 2) - 1,
+	};
+	const size_t unitByteSize = sizeof(mcl::fp::Unit);
+	for (size_t i = 0; i < CYBOZU_NUM_OF_ARRAY(tbl); i++) {
+		const mpz_class& x = tbl[i];
+		const mcl::fp::Unit *px = mcl::gmp::getUnit(x);
+		const size_t xn = mcl::gmp::getUnitSize(x);
+		const size_t xByteSize = xn * unitByteSize;
+		const size_t fpByteSize = unitByteSize * Fp::getOp().N;
+		Fp y;
+		bool b;
+		y.setArray(&b, px, xn, mcl::fp::Mod);
+		bool expected = xByteSize <= fpByteSize * 2;
+		CYBOZU_TEST_EQUAL(b, expected);
+		if (!b) continue;
+		CYBOZU_TEST_EQUAL(y.getMpz(), x % p);
+	}
+}
+
 CYBOZU_TEST_AUTO(set64bit)
 {
 	Fp::init("0x1000000000000000000f");
@@ -911,6 +948,7 @@ void sub(mcl::fp::Mode mode)
 		powGmp();
 		setArrayTest1();
 		setArrayMaskTest1();
+		setArrayModTest();
 		getUint64Test();
 		getInt64Test();
 		divBy2Test();