diff --git a/secop/modules.py b/secop/modules.py
index d6321ec..827740b 100644
--- a/secop/modules.py
+++ b/secop/modules.py
@@ -478,7 +478,7 @@ class Module(HasAccessibles):
         # Modify units AFTER applying the cfgdict
         mainvalue = self.parameters.get('value')
         if mainvalue:
-            mainunit = ['value'].datatype.unit
+            mainunit = mainvalue.datatype.unit
             if mainunit:
                 for pname, pobj in self.parameters.items():
                     pobj.datatype.set_main_unit(mainunit)