diff --git a/ChemistryLib/PhreeqcIO.cpp b/ChemistryLib/PhreeqcIO.cpp
index c81d722f23538845f38feedb0973f6dd768e520d..430fda2dc851686d06fe3c4ecccdca80aac1b4ce 100644
--- a/ChemistryLib/PhreeqcIO.cpp
+++ b/ChemistryLib/PhreeqcIO.cpp
@@ -29,8 +29,6 @@ std::ostream& operator<<(std::ostream& os,
               std::ostream_iterator<DataBlock>(os));
     return os;
 }
-
-static const int phreeqc_instance_id = 0;
 }  // namespace
 
 PhreeqcIO::PhreeqcIO(
diff --git a/ChemistryLib/PhreeqcIO.h b/ChemistryLib/PhreeqcIO.h
index a6f6b5182c02950f3190b31e720ba6b75c93fe71..5ec9dbb5598d008fa2d6547eebecdd03a4e2f1ff 100644
--- a/ChemistryLib/PhreeqcIO.h
+++ b/ChemistryLib/PhreeqcIO.h
@@ -71,5 +71,6 @@ private:
     std::vector<std::pair<int, std::string>> const&
         _process_id_to_component_name_map;
     double _dt = std::numeric_limits<double>::quiet_NaN();
+    const int phreeqc_instance_id = 0;
 };
 }  // namespace ChemistryLib