diff --git a/LDDsimulation/domainPatch.py b/LDDsimulation/domainPatch.py
index bb9974426c93073626115d9523a1515ac2f6c449..8d66b564807a7dd0af207a6c581986b08f8c00ae 100644
--- a/LDDsimulation/domainPatch.py
+++ b/LDDsimulation/domainPatch.py
@@ -715,8 +715,41 @@ class DomainPatch(df.SubDomain):
     def _calc_interface_has_common_dof_indices(self):
         """ populate dictionary self._interface_has_common_dof_indices
 
-        Determin for each interface in self.has_interface the dof indices
+        Determin for each interface in self.has_interface the dof indices that
+        also belong to another interface and store them in the dictionary
+        self._interface_has_common_dof_indices
+        This method populates the dictionary
+            self._interface_has_common_dof_indices
         """
+        for interf_ind, interf_dofs in self._dof_indices_of_interface.items():
+            # initialise bool numpy arry for the search.
+            if self.isRichards:
+                is_part_of_neighbour_interface_w = np.zeros(interf_dofs['wetting'].size, dtype=bool)
+            else:
+                is_part_of_neighbour_interface_w = np.zeros(interf_dofs['wetting'].size, dtype=bool)
+                is_part_of_neighbour_interface_nw = np.zeros(interf_dofs['nonwetting'].size, dtype=bool)
+
+            for other_interf_ind, other_interf_dofs in self._dof_indices_of_interface.items():
+                if other_interf_ind is not interf_ind:
+                    if self.isRichards:
+                        is_part_of_neighbour_interface_w += np.isin(interf_dofs['wetting'], other_interf_dofs['wetting'], assume_unique=True)
+                    else:
+                        is_part_of_neighbour_interface_w += np.isin(interf_dofs['wetting'], other_interf_dofs['wetting'], assume_unique=True)
+                        is_part_of_neighbour_interface_nw += np.isin(interf_dofs['nonwetting'], other_interf_dofs['nonwetting'], assume_unique=True)
+            # this carries a numpyarray of the indices which belong to other
+            # interfaces, too
+            self._interface_has_common_dof_indices.update({interf_ind: dict()})
+            if self.isRichards:
+                self._interface_has_common_dof_indices[interf_ind].update(
+                    {'wetting': interf_dofs['wetting'][is_part_of_neighbour_interface_w]}
+                )
+            else:
+                self._interface_has_common_dof_indices[interf_ind].update(
+                    {'wetting': interf_dofs['wetting'][is_part_of_neighbour_interface_w]},
+                    {'nonwetting': interf_dofs['nonwetting'][is_part_of_neighbour_interface_nw]}
+                )
+
+
 
 
 # END OF CLASS DomainPatch