--- a/twext/enterprise/dal/parseschema.py
+++ b/twext/enterprise/dal/parseschema.py
@@ -721,7 +721,7 @@
     not whitespace.
     """
     # comment has None is_whitespace() result.  intentional?
-    return (not isinstance(token, Comment) and not token.is_whitespace())
+    return (not isinstance(token, Comment) and not token.is_whitespace)
 
 
 def iterSignificant(tokenList):