diff --git a/secop/params.py b/secop/params.py
index af26423..310a195 100644
--- a/secop/params.py
+++ b/secop/params.py
@@ -120,7 +120,7 @@ class Parameter(Accessible):
                                  NoneOr(BoolType()), export=False, default=None, mandatory=False, settable=False),
     }
 
-    def __init__(self, description, datatype, ctr=None, unit=None, **kwds):
+    def __init__(self, description, datatype, *, ctr=None, unit=None, **kwds):
 
         if ctr is not None:
             self.ctr = ctr
@@ -227,13 +227,15 @@ class Override(CountedObj):
     note: overrides are applied by the metaclass during class creating
     reorder= True: use position of Override instead of inherited for the order
     """
-    def __init__(self, description="", reorder=False, **kwds):
+    def __init__(self, description="", datatype=None, *, reorder=False, **kwds):
         super(Override, self).__init__()
         self.kwds = kwds
         self.reorder = reorder
-        # allow to override description without keyword
+        # allow to override description and datatype without keyword
         if description:
             self.kwds['description'] = description
+        if datatype is not None:
+            self.kwds['datatype'] = datatype
         # for now, do not use the Override ctr
         # self.kwds['ctr'] = self.ctr