diff --git a/ostap/fitting/fit2d.py b/ostap/fitting/fit2d.py
index d5cd4ae4..c314e1dd 100755
--- a/ostap/fitting/fit2d.py
+++ b/ostap/fitting/fit2d.py
@@ -298,9 +298,9 @@ def __init__ ( self , name , shape , xvar , yvar , tag = 0 ) :
 
         if isinstance ( shape , ROOT.TH2 ) and 2 == shape.dim () :
             
-            self.histo = shape
-            shape      = Ostap.Math.Histo2D     ( shape )
-            tag        = Ostap.Utils.hash_histo ( shape ) 
+            self.histo_obj = shape
+            shape          = Ostap.Math.Histo2D     ( shape )
+            tag            = Ostap.Utils.hash_histo ( shape ) 
             
         elif hasattr ( shape , 'tag' ) and not tag :