diff --git a/prody/ensemble/pdbensemble.py b/prody/ensemble/pdbensemble.py
index 34ce1d22e..1ee7c67ca 100644
--- a/prody/ensemble/pdbensemble.py
+++ b/prody/ensemble/pdbensemble.py
@@ -289,6 +289,7 @@ def addCoordset(self, coords, weights=None, label=None, **kwargs):
        
         if not n_atoms:
             self._n_atoms = n_nodes
+            n_atoms = self._n_atoms
 
         if n_nodes == n_select and self.isSelected():
             full_coords = np.repeat(self._coords[np.newaxis, :, :], n_csets, axis=0)