diff --git a/include/mcl/fp_generator.hpp b/include/mcl/fp_generator.hpp
index 961c4ca..59e2b60 100644
--- a/include/mcl/fp_generator.hpp
+++ b/include/mcl/fp_generator.hpp
@@ -121,6 +121,8 @@ if (rm.isReg()) { \
 	op(qword [rm.getMem()], r); \
 }
 
+namespace fp {
+
 struct FpGenerator : Xbyak::CodeGenerator {
 	typedef Xbyak::RegExp RegExp;
 	typedef Xbyak::Reg64 Reg64;
@@ -1641,6 +1643,6 @@ private:
 	}
 };
 
-} // mcl
+} } // mcl::fp
 
 #endif
diff --git a/include/mcl/op.hpp b/include/mcl/op.hpp
index 6f2aadf..5d4ab12 100644
--- a/include/mcl/op.hpp
+++ b/include/mcl/op.hpp
@@ -16,10 +16,10 @@
 
 namespace mcl {
 
-struct FpGenerator;
-
 namespace fp {
 
+struct FpGenerator;
+
 const size_t maxOpUnitN = (MCL_MAX_OP_BIT_N + UnitBitN - 1) / UnitBitN;
 
 struct Op;
diff --git a/test/fp_generator_test.cpp b/test/fp_generator_test.cpp
index 9a61ab2..28ad51c 100644
--- a/test/fp_generator_test.cpp
+++ b/test/fp_generator_test.cpp
@@ -110,7 +110,7 @@ static inline std::ostream& operator<<(std::ostream& os, const Int& x)
 	return os << x.toStr();
 }
 
-void testAddSub(const mcl::FpGenerator& fg, int pn)
+void testAddSub(const mcl::fp::FpGenerator& fg, int pn)
 {
 	Fp x, y;
 	Int mx(pn), my(pn);
@@ -135,7 +135,7 @@ void testAddSub(const mcl::FpGenerator& fg, int pn)
 	}
 }
 
-void testNeg(const mcl::FpGenerator& fg, int pn)
+void testNeg(const mcl::fp::FpGenerator& fg, int pn)
 {
 	Fp x;
 	Int mx(pn), my(pn);
@@ -154,7 +154,7 @@ void testNeg(const mcl::FpGenerator& fg, int pn)
 	}
 }
 
-void testMulI(const mcl::FpGenerator& fg, int pn)
+void testMulI(const mcl::fp::FpGenerator& fg, int pn)
 {
 	cybozu::XorShift rg;
 	for (int i = 0; i < 100; i++) {
@@ -181,7 +181,7 @@ void testMulI(const mcl::FpGenerator& fg, int pn)
 	}
 }
 
-void testShr1(const mcl::FpGenerator& fg, int pn)
+void testShr1(const mcl::fp::FpGenerator& fg, int pn)
 {
 	cybozu::XorShift rg;
 	for (int i = 0; i < 100; i++) {
@@ -204,7 +204,7 @@ void test(const char *pStr)
 	uint64_t p[MAX_N];
 	const int pn = convertToArray(p, pStr);
 	printf("pn=%d\n", pn);
-	mcl::FpGenerator fg;
+	mcl::fp::FpGenerator fg;
 	fg.init(p, pn);
 	testAddSub(fg, pn);
 	testNeg(fg, pn);