diff --git a/grudge/symbolic/operators.py b/grudge/symbolic/operators.py
index babccafa211160414358e9617a7996eb22a61bed..405db3e1b044e1438c0ef9b8799fcd9dd919bb55 100644
--- a/grudge/symbolic/operators.py
+++ b/grudge/symbolic/operators.py
@@ -624,9 +624,9 @@ class RefFaceMassOperator(ElementwiseLinearOperator):
         assert afgrp.nelements == nfaces * volgrp.nelements
 
         matrix = np.empty(
-                (volgrp.nunit_nodes,
+                (volgrp.nunit_dofs,
                     nfaces,
-                    afgrp.nunit_nodes),
+                    afgrp.nunit_dofs),
                 dtype=dtype)
 
         from modepy.tools import UNIT_VERTICES