diff --git a/docs/manual/references.rst b/docs/manual/references.rst
index 97c7ef2b..80eaf2d1 100644
--- a/docs/manual/references.rst
+++ b/docs/manual/references.rst
@@ -19,8 +19,12 @@ References
 .. [JoOM06] Jönsthövel, T. B., C. W. Oosterlee, and W. A. Mulder, 2006,
    Improving multigrid for 3-D electro-magnetic diffusion on stretched grids:
    European Conference on Computational Fluid Dynamics; UUID:
-   `df65da5c-e43f-47ab-b80d-2f8ee7f35464
-   <http://resolver.tudelft.nl/uuid:df65da5c-e43f-47ab-b80d-2f8ee7f35464>`_.
+   `632b503b-149a-47c1-a6b2-2f98f8703b48
+   <https://resolver.tudelft.nl/uuid:632b503b-149a-47c1-a6b2-2f98f8703b48>`_.
+
+   ..
+       df65da5c-e43f-47ab-b80d-2f8ee7f35464  # Old uuid
+
 .. [Hack85] Hackbusch, W., 1985, Multi-grid methods and applications: Springer,
    Berlin, Heidelberg, Volume 4 of Springer Series in Computational
    Mathematics; DOI: `10.1007/978- 3-662-02427-0 <https://doi.org/10.1007/978-
diff --git a/emg3d/surveys.py b/emg3d/surveys.py
index d76b24dc..fe158872 100644
--- a/emg3d/surveys.py
+++ b/emg3d/surveys.py
@@ -716,15 +716,15 @@ def _rec_types_coord(self, source):
     @property
     def isfinite(self):
         """Return indices of the finite data."""
-        if hasattr(self, '_isfinite'):
-            return self._isfinite
-        else:
+        if not hasattr(self, '_isfinite'):
             finite = np.isfinite(self.data.observed.data)
-            # Only set the marker if there is any data.
+            # Only set the attribute if there is any data.
             # Otherwise, this was called before observations were added.
             if finite.sum() > 0:
                 self._isfinite = finite
-            return finite
+        else:
+            finite = self._isfinite
+        return finite
 
     def finite_data(self, data='observed'):
         """Return finite elements of selected `data`."""