diff --git a/modules/gui/pymod/dng/menu.py b/modules/gui/pymod/dng/menu.py
index de943d3225a2c25ea3f6a42b0aefbb6969e3f9ad..75d2ae2ba34ba30328cf57a6fef4656bcf4fbba0 100644
--- a/modules/gui/pymod/dng/menu.py
+++ b/modules/gui/pymod/dng/menu.py
@@ -191,13 +191,14 @@ class SceneMenu(QMenu):
       i += 1
       gfx_ent_2 = sel.GetActiveNode(i)
     sd = superpositiondialog.SuperpositionDialog(gfx_ent_1, gfx_ent_2)
-    if sd.reference == 0:
-      gfx_ent_1.UpdatePositions()
-      gfx.Scene().CenterOn(gfx_ent_1)
-    else:
-      gfx_ent_2.UpdatePositions()
-      gfx.Scene().CenterOn(gfx_ent_2)
-    LogScript('RMSD: %.3f'%sd.rmsd)
+    if sd.rmsd != None:
+      if sd.reference == 0:
+        gfx_ent_1.UpdatePositions()
+        gfx.Scene().CenterOn(gfx_ent_1)
+      else:
+        gfx_ent_2.UpdatePositions()
+        gfx.Scene().CenterOn(gfx_ent_2)
+      LogScript('RMSD: %.3f'%sd.rmsd)
 
 class WindowMenu(QMenu):
   def __init__(self, parent=None):
diff --git a/modules/gui/pymod/dng/superpositiondialog.py b/modules/gui/pymod/dng/superpositiondialog.py
index 4c22b4c9658ba7885bea4e30f2683eb8208c3404..3928adf7d75af3f4e36b00e84de43a33b507ad91 100644
--- a/modules/gui/pymod/dng/superpositiondialog.py
+++ b/modules/gui/pymod/dng/superpositiondialog.py
@@ -118,7 +118,7 @@ class SuperpositionDialog(QDialog):
 
   def __init__(self, ent_one, ent_two, parent=None):
     # class variables
-    self.rmsd = 0.0
+    self.rmsd = None
     self._mmethod_dict = {'number': 'number',
                           'index': 'index',
                           'local alignment': 'local-aln',
@@ -302,7 +302,6 @@ class SuperpositionDialog(QDialog):
       self._chain_one.SetItems(self.ent_two, self.gfx_two)
       self._chain_two.SetItems(self.ent_one, self.gfx_one)
       self.reference = 1;
-    return
 
   def _MatchMethods(self):
     methods=QComboBox(self)