diff --git a/src/misc/hashtable.hpp b/src/misc/hashtable.hpp
--- a/src/misc/hashtable.hpp
+++ b/src/misc/hashtable.hpp
@@ -12,6 +12,8 @@
 #ifndef  HASHTABLE_HPP
 #define  HASHTABLE_HPP
 
+#include "../core/math_func.hpp"
+
 template <class Titem_>
 struct CHashTableSlotT
 {