diff --git a/pyerrors/obs.py b/pyerrors/obs.py
index 57b8ae17..0d3f5ebf 100644
--- a/pyerrors/obs.py
+++ b/pyerrors/obs.py
@@ -978,7 +978,7 @@ def _filter_zeroes(names, deltas, idl, eps=Obs.filter_eps):
     if new_names:
         return (new_names, new_deltas, new_idl)
     else:
-        return (new_names, new_deltas, new_idl)
+        return (names, deltas, idl)
 
 
 def derived_observable(func, data, **kwargs):