diff --git a/dafoam/mphys/mphys_dafoam.py b/dafoam/mphys/mphys_dafoam.py
index bbca1fb7..83df186f 100644
--- a/dafoam/mphys/mphys_dafoam.py
+++ b/dafoam/mphys/mphys_dafoam.py
@@ -137,6 +137,10 @@ def get_number_of_nodes(self, groupName=None):
                         nodes += 1 + parameters["nNodes"]
         return nodes
 
+    def get_ndof(self):
+        # The number of degrees of freedom used at each output location.
+        return -1
+
 
 class DAFoamGroup(Group):
     """