diff --git a/src/fp.cpp b/src/fp.cpp
index eb8a7de..3a70db5 100644
--- a/src/fp.cpp
+++ b/src/fp.cpp
@@ -3,6 +3,10 @@
 #include <cybozu/sha2.hpp>
 #include <cybozu/endian.hpp>
 #include <mcl/conversion.hpp>
+#if defined(__EMSCRIPTEN__) && MCL_SIZEOF_UNIT == 4
+#define FOR_WASM
+#include "low_funct.hpp"
+#endif
 
 #if defined(MCL_STATIC_CODE) || defined(MCL_USE_XBYAK) || (defined(MCL_USE_LLVM) && (CYBOZU_HOST == CYBOZU_HOST_INTEL))
 
@@ -268,6 +272,20 @@ void setOp2(Op& op)
 	} else {
 		op.fp_add = Add<N, false, Tag>::f;
 		op.fp_sub = Sub<N, false, Tag>::f;
+#ifdef FOR_WASM
+		switch (N) {
+		case 8:
+			op.fp_add = mcl::addModT<8>;
+			op.fp_sub = mcl::subModT<8>;
+			break;
+		case 12:
+			op.fp_add = mcl::addModT<12>;
+			op.fp_sub = mcl::subModT<12>;
+			break;
+		default:
+			break;
+		}
+#endif
 	}
 	if (op.isMont) {
 		if (op.isFullBit) {
diff --git a/src/low_funct.hpp b/src/low_funct.hpp
new file mode 100644
index 0000000..a9751dd
--- /dev/null
+++ b/src/low_funct.hpp
@@ -0,0 +1,67 @@
+#pragma once
+/**
+	@file
+	@author MITSUNARI Shigeo(@herumi)
+	@license modified new BSD license
+	http://opensource.org/licenses/BSD-3-Clause
+*/
+#include <stdint.h>
+#include <stdlib.h>
+
+// for 32bit not full version
+
+namespace mcl {
+
+template<size_t N>
+void copyT(uint32_t *y, const uint32_t *x)
+{
+	for (size_t i = 0; i < N; i++) {
+		y[i] = x[i];
+	}
+}
+
+template<size_t N>
+void addT(uint32_t *z, const uint32_t *x, const uint32_t *y)
+{
+	bool c = false;
+	for (size_t i = 0; i < N; i++) {
+		uint64_t v = uint64_t(x[i]) + y[i] + c;
+		z[i] = uint32_t(v);
+		c = (v >> 32) != 0;
+	}
+}
+
+template<size_t N>
+bool subT(uint32_t *z, const uint32_t *x, const uint32_t *y)
+{
+	bool c = false;
+	for (size_t i = 0; i < N; i++) {
+		uint64_t v = uint64_t(x[i]) - y[i] - c;
+		z[i] = uint32_t(v);
+		c = (v >> 32) != 0;
+	}
+	return c;
+}
+
+template<size_t N>
+void addModT(uint32_t *z, const uint32_t *x, const uint32_t *y, const uint32_t *p)
+{
+	uint32_t t[N];
+	addT<N>(z, x, y);
+	bool c = subT<N>(t, z, p);
+	if (!c) {
+		copyT<N>(z, t);
+	}
+}
+
+template<size_t N>
+void subModT(uint32_t *z, const uint32_t *x, const uint32_t *y, const uint32_t *p)
+{
+	bool c = subT<N>(z, x, y);
+	if (c) {
+		addT<N>(z, z, p);
+	}
+}
+
+} // mcl
+