diff --git a/grudge/discretization.py b/grudge/discretization.py
index 7fb4562df39a35c8c5278f642b47b8fd642bc654..300b5fbc362b4d84ff940a72efd0d686d99dc135 100644
--- a/grudge/discretization.py
+++ b/grudge/discretization.py
@@ -91,7 +91,9 @@ class Discretization(object):
 
     def is_volume_where(self, where):
         from grudge import sym
-        return where == sym.VTAG_ALL
+        return (
+                where is None
+                or where == sym.VTAG_ALL)
 
 
 # vim: foldmethod=marker