diff --git a/test/lightweight_test_with_test.cpp b/test/lightweight_test_with_test.cpp
index 9f3c42b..461d1e6 100644
--- a/test/lightweight_test_with_test.cpp
+++ b/test/lightweight_test_with_test.cpp
@@ -8,16 +8,14 @@
 // http://www.boost.org/LICENSE_1_0.txt
 //
 
-#include <cmath>
-#include <functional>
-#include <vector>
 #include <boost/core/lightweight_test.hpp>
+#include <cmath>
 
 template <typename T>
 struct with_tolerance
 {
     with_tolerance(T tolerance) : tolerance(tolerance) {}
-    bool operator()(T lhs, T rhs)
+    bool operator()(T lhs, T rhs) const
     {
         return (std::abs(lhs - rhs) <= tolerance);
     }