diff --git a/copasi_petab_importer/convert_benchmark.py b/copasi_petab_importer/convert_benchmark.py
index bcb4fe1..f5ec03f 100644
--- a/copasi_petab_importer/convert_benchmark.py
+++ b/copasi_petab_importer/convert_benchmark.py
@@ -78,8 +78,8 @@ def add_fit_items(parameters):
 
         # if we found it, get its internal identifier and create the item
         item = problem.addOptItem(cn)
-        item.setLowerBound(COPASI.CCommonName(str(lower)))   # set the lower
-        item.setUpperBound(COPASI.CCommonName(str(upper)))   # and upper bound
+        item.setLowerBound(COPASI.CRegisteredCommonName(str(lower)))   # set the lower
+        item.setUpperBound(COPASI.CRegisteredCommonName(str(upper)))   # and upper bound
         item.setStartValue(value)                # as well as the initial value
 
 
diff --git a/copasi_petab_importer/convert_petab.py b/copasi_petab_importer/convert_petab.py
index ef4ba2e..f61ae09 100644
--- a/copasi_petab_importer/convert_petab.py
+++ b/copasi_petab_importer/convert_petab.py
@@ -750,10 +750,10 @@ def add_fit_items(self, parameters):
             item = problem.addOptItem(cn)
             if np.isnan(lower):
                 lower = math.pow(10, -6)
-            item.setLowerBound(COPASI.CCommonName(str(lower)))
+            item.setLowerBound(COPASI.CRegisteredCommonName(str(lower)))
             if np.isnan(upper):
                 upper = math.pow(10, 6)
-            item.setUpperBound(COPASI.CCommonName(str(upper)))
+            item.setUpperBound(COPASI.CRegisteredCommonName(str(upper)))
             item.setStartValue(value)  # as well as the initial value
 
         # create experiment specific fit items
@@ -799,10 +799,10 @@ def add_fit_items(self, parameters):
                 item = problem.addFitItem(cn)
                 if np.isnan(lower):
                     lower = math.pow(10, -6)
-                item.setLowerBound(COPASI.CCommonName(str(lower)))
+                item.setLowerBound(COPASI.CRegisteredCommonName(str(lower)))
                 if np.isnan(upper):
                     upper = math.pow(10, 6)
-                item.setUpperBound(COPASI.CCommonName(str(upper)))
+                item.setUpperBound(COPASI.CRegisteredCommonName(str(upper)))
                 item.setStartValue(value)  # as well as the initial value
                 item.addExperiment(self.experiment_to_key[condition])