diff --git a/dumux/common/monotonecubicspline.hh b/dumux/common/monotonecubicspline.hh
index 0af5c0ad4377445ede38b85d2f3417dfef14101b..dc3ae15bdae1a6a4f8fd1a04f9bd6a86507292cc 100644
--- a/dumux/common/monotonecubicspline.hh
+++ b/dumux/common/monotonecubicspline.hh
@@ -62,7 +62,7 @@ public:
      * \param x a vector of x-coordinates
      * \param y a vector of y-coordinates
      */
-    MonotoneCubicSpline(const std::vector<Scalar>& x, const std::vector<Scalar> y)
+    MonotoneCubicSpline(const std::vector<Scalar>& x, const std::vector<Scalar>& y)
     {
         // check some requirements
         assert (x.size() == y.size());