diff --git a/examples/eigen/eigen.cpp b/examples/eigen/eigen.cpp
index 55a3b99..5d966d4 100644
--- a/examples/eigen/eigen.cpp
+++ b/examples/eigen/eigen.cpp
@@ -1,10 +1,9 @@
 #include <Eigen/Dense>
+#include <pico_tree/eigen_adaptor.hpp>
 #include <pico_tree/kd_tree.hpp>
 #include <point.hpp>
 #include <scoped_timer.hpp>
 
-#include "eigen_adaptor.hpp"
-
 using Index = int;
 using Scalar = double;
 
diff --git a/examples/eigen/eigen_adaptor.hpp b/src/pico_tree/eigen_adaptor.hpp
similarity index 89%
rename from examples/eigen/eigen_adaptor.hpp
rename to src/pico_tree/eigen_adaptor.hpp
index 675794f..878e2bb 100644
--- a/examples/eigen/eigen_adaptor.hpp
+++ b/src/pico_tree/eigen_adaptor.hpp
@@ -1,7 +1,5 @@
 #pragma once
 
-#include <Eigen/Dense>
-
 namespace pico_tree {
 
 namespace internal {
@@ -26,9 +24,8 @@ class EigenAdaptorBase<Index_, EigenMatrix, false> {
   }
 
   //! Returns dimension \p dim of point \p point.
-  template <typename Derived>
-  inline Scalar operator()(
-      Eigen::MatrixBase<Derived> const& point, Index const dim) const {
+  template <typename Point>
+  inline Scalar operator()(Point const& point, Index const dim) const {
     return point(dim);
   }
 
@@ -59,9 +56,8 @@ class EigenAdaptorBase<Index_, EigenMatrix, true> {
   }
 
   //! Returns dimension \p dim of point \p point.
-  template <typename Derived>
-  inline Scalar operator()(
-      Eigen::MatrixBase<Derived> const& point, Index const dim) const {
+  template <typename Point>
+  inline Scalar operator()(Point const& point, Index const dim) const {
     return point(dim);
   }