diff --git a/matrix/integration.hpp b/matrix/integration.hpp
index 67eae7a453..afc0cb7556 100644
--- a/matrix/integration.hpp
+++ b/matrix/integration.hpp
@@ -6,12 +6,12 @@ namespace matrix {
 
 template<typename Type, size_t M, size_t N>
 int integrate_rk4(
-    Vector<Type, M> (*f)(Type, const Vector<Type, M> &x, const Vector<Type, N> & u),
-    const Vector<Type, M> & y0,
-    const Vector<Type, N> & u,
+    Vector<Type, M> (*f)(Type, const Matrix<Type, M, 1> &x, const Matrix<Type, N, 1> & u),
+    const Matrix<Type, M, 1> & y0,
+    const Matrix<Type, N, 1> & u,
     Type t0,
     Type h,
-    Vector<Type, M> & y1
+    Matrix<Type, M, 1> & y1
 )
 {
     // https://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods