diff --git a/include/mcl/lagrange.hpp b/include/mcl/lagrange.hpp
index feca80d..18e0597 100644
--- a/include/mcl/lagrange.hpp
+++ b/include/mcl/lagrange.hpp
@@ -63,15 +63,20 @@ void LagrangeInterpolation(bool *pb, G& out, const F *S, const G *vec, size_t k)
 
 /*
 	out = f(x) = c[0] + c[1] * x + c[2] * x^2 + ... + c[cSize - 1] * x^(cSize - 1)
-	@retval 0 if succeed else -1
+	@retval 0 if succeed else -1 (if cSize == 0)
 */
 template<class G, class T>
 void evaluatePolynomial(bool *pb, G& out, const G *c, size_t cSize, const T& x)
 {
-	if (cSize < 2) {
+	if (cSize == 0) {
 		*pb = false;
 		return;
 	}
+	if (cSize == 1) {
+		out = c[0];
+		*pb = true;
+		return;
+	}
 	G y = c[cSize - 1];
 	for (int i = (int)cSize - 2; i >= 0; i--) {
 		G::mul(y, y, x);
diff --git a/test/bench.hpp b/test/bench.hpp
index 12868d3..cc1639e 100644
--- a/test/bench.hpp
+++ b/test/bench.hpp
@@ -187,4 +187,6 @@ void testLagrange()
 	CYBOZU_TEST_EQUAL(s, c[0]);
 	mcl::LagrangeInterpolation(s, x, y, 1);
 	CYBOZU_TEST_EQUAL(s, y[0]);
+	mcl::evaluatePolynomial(y[0], c, 1, x[0]);
+	CYBOZU_TEST_EQUAL(y[0], c[0]);
 }