diff --git a/test/realizations/catchments/Bmi_C_Formulation_Test.cpp b/test/realizations/catchments/Bmi_C_Formulation_Test.cpp
index 9a23441090..9c5dfd2900 100644
--- a/test/realizations/catchments/Bmi_C_Formulation_Test.cpp
+++ b/test/realizations/catchments/Bmi_C_Formulation_Test.cpp
@@ -73,7 +73,7 @@ class Bmi_C_Formulation_Test : public ::testing::Test {
         return formulation.get_model_type_name();
     }
 
-    static double get_friend_var_value_as_double(Bmi_C_Formulation& formulation, const string& var_name) {
+    static double get_friend_var_value_as_double(Bmi_C_Formulation& formulation, const std::string& var_name) {
         return formulation.get_var_value_as_double(var_name);
     }
 
diff --git a/test/realizations/catchments/Bmi_Fortran_Formulation_Test.cpp b/test/realizations/catchments/Bmi_Fortran_Formulation_Test.cpp
index 5b6c850e3c..f1de49db13 100644
--- a/test/realizations/catchments/Bmi_Fortran_Formulation_Test.cpp
+++ b/test/realizations/catchments/Bmi_Fortran_Formulation_Test.cpp
@@ -71,7 +71,7 @@ class Bmi_Fortran_Formulation_Test : public ::testing::Test {
         return formulation.get_model_type_name();
     }
 
-    static double get_friend_var_value_as_double(Bmi_Fortran_Formulation& formulation, const string& var_name) {
+    static double get_friend_var_value_as_double(Bmi_Fortran_Formulation& formulation, const std::string& var_name) {
         return formulation.get_var_value_as_double(var_name);
     }