diff --git a/core/src/io/hamiltonian/Biaxial_Anisotropy.cpp b/core/src/io/hamiltonian/Biaxial_Anisotropy.cpp
index 9c1cb989b..b8ff089b9 100644
--- a/core/src/io/hamiltonian/Biaxial_Anisotropy.cpp
+++ b/core/src/io/hamiltonian/Biaxial_Anisotropy.cpp
@@ -3,6 +3,7 @@
 #include <io/Filter_File_Handle.hpp>
 #include <io/Tableparser.hpp>
 
+#include <iso646.h>
 #include <vector>
 
 using Utility::Log_Level, Utility::Log_Sender;