diff --git a/ChemistryLib/PhreeqcIOData/CreateOutput.h b/ChemistryLib/PhreeqcIOData/CreateOutput.h
index ce178b6a46b1f2f14be938c5c8cab2c1f0e1113e..8a5050e4277557345c8a8bac0d748c80580d6bdf 100644
--- a/ChemistryLib/PhreeqcIOData/CreateOutput.h
+++ b/ChemistryLib/PhreeqcIOData/CreateOutput.h
@@ -11,6 +11,7 @@
 #pragma once
 
 #include <memory>
+#include <string>
 #include <vector>
 
 namespace ChemistryLib