diff --git a/src/IPhreeqc.hpp b/src/IPhreeqc.hpp
index 364ea8ac..42a495b2 100644
--- a/src/IPhreeqc.hpp
+++ b/src/IPhreeqc.hpp
@@ -889,6 +889,8 @@ protected:
 	bool get_sel_out_file_on(int n)const;
 	std::string sel_file_name(int n_user);
 
+	std::string create_file_name(const char *prefix, const char *suffix);
+
 	bool get_sel_out_string_on(int n)const;
 
 protected: