diff --git a/internal/ceres/polynomial_test.cc b/internal/ceres/polynomial_test.cc
index f56352f..7c992fa 100644
--- a/internal/ceres/polynomial_test.cc
+++ b/internal/ceres/polynomial_test.cc
@@ -225,7 +225,8 @@
   Vector polynomial(1);
   polynomial(0) = 1.0;
   const Vector derivative = DifferentiatePolynomial(polynomial);
-  EXPECT_EQ(derivative.rows(), 0);
+  EXPECT_EQ(derivative.rows(), 1);
+  EXPECT_EQ(derivative(0), 0);
 }
 
 TEST(Polynomial, DifferentiateQuadraticPolynomial) {