diff --git a/include/mcl/fp.hpp b/include/mcl/fp.hpp
index 1cfcfd8..6703daf 100644
--- a/include/mcl/fp.hpp
+++ b/include/mcl/fp.hpp
@@ -38,8 +38,6 @@ struct ZnTag;
 
 namespace fp {
 
-// copy src to dst as little endian
-void copyUnitToByteAsLE(uint8_t *dst, const Unit *src, size_t byteSize);
 // copy src to dst as little endian
 void copyByteToUnitAsLE(Unit *dst, const uint8_t *src, size_t byteSize);
 
diff --git a/src/fp.cpp b/src/fp.cpp
index 7362770..365da45 100644
--- a/src/fp.cpp
+++ b/src/fp.cpp
@@ -632,22 +632,6 @@ bool Op::init(const mpz_class& _p, size_t maxBitSize, int _xi_a, Mode mode, size
 	return fp::initForMont(*this, p, mode);
 }
 
-void copyUnitToByteAsLE(uint8_t *dst, const Unit *src, size_t byteSize)
-{
-	while (byteSize >= sizeof(Unit)) {
-		setUnitAsLE(dst, *src++);
-		dst += sizeof(Unit);
-		byteSize -= sizeof(Unit);
-	}
-	if (byteSize == 0) return;
-	Unit x = *src;
-	while (byteSize) {
-		*dst++ = static_cast<uint8_t>(x);
-		x >>= 8;
-		byteSize--;
-	}
-}
-
 void copyByteToUnitAsLE(Unit *dst, const uint8_t *src, size_t byteSize)
 {
 	while (byteSize >= sizeof(Unit)) {
diff --git a/test/fp_test.cpp b/test/fp_test.cpp
index 3f15a0d..8883e69 100644
--- a/test/fp_test.cpp
+++ b/test/fp_test.cpp
@@ -1041,7 +1041,7 @@ CYBOZU_TEST_AUTO(main)
 #endif
 }
 
-CYBOZU_TEST_AUTO(copyUnitToByteAsLE)
+CYBOZU_TEST_AUTO(copyByteToUnitAsLE)
 {
 	using namespace mcl::fp;
 #if MCL_SIZEOF_UNIT == 4
@@ -1050,12 +1050,6 @@ CYBOZU_TEST_AUTO(copyUnitToByteAsLE)
 	const Unit src[] = { uint64_t(0xaabbccdd12345678ull), uint64_t(0x87654321ffeeddcc) };
 #endif
 	const uint8_t ok[] = { 0x78, 0x56, 0x34, 0x12, 0xdd, 0xcc, 0xbb, 0xaa, 0xcc, 0xdd, 0xee, 0xff, 0x21, 0x43, 0x65, 0x87 };
-	const size_t okN = CYBOZU_NUM_OF_ARRAY(ok);
-	for (size_t i = 0; i < okN; i++) {
-		uint8_t buf[okN] = {};
-		copyUnitToByteAsLE(buf, src, i);
-		CYBOZU_TEST_EQUAL_ARRAY(ok, buf, i);
-	}
 	mcl::fp::Unit dst[2];
 	for (size_t i = 1; i <= sizeof(dst); i++) {
 		memset(dst, 0xff, sizeof(dst));