diff --git a/Ch 4. Trees and Graphs/C++14/treetestutils.hpp b/Ch 4. Trees and Graphs/C++14/treetestutils.hpp
index d650881..ffe8f4b 100644
--- a/Ch 4. Trees and Graphs/C++14/treetestutils.hpp	
+++ b/Ch 4. Trees and Graphs/C++14/treetestutils.hpp	
@@ -7,6 +7,7 @@
 #include <iostream>
 #include <iomanip>
 #include <memory>
+#include <cmath>
 
 template <typename T, bool NodeWithParent,
           template<typename, bool> class Node>