--- a/src/include/interpolator.hpp
+++ b/src/include/interpolator.hpp
@@ -25,6 +25,8 @@
 using std::map;
 using boost::shared_ptr;
 
+class vtkplot;
+
 //FIXME: Break this up into an ansatz class and an interpolator
 //class. 
 /*! \brief An interpolator \f$ \displaystyle u(x) = \sum_{\xi \in
@@ -190,6 +192,9 @@
    *   values that the interpolator takes on that point.
    */
   void into_os(std::ostream& os) const;
+
+  ///Needed in order to plot the data
+  friend class vtkplot;
     
 private:
   ///Once the matrix is defined, this function inverts it.