diff --git a/src/OFS/ObjectManager.py b/src/OFS/ObjectManager.py
index ba6be85e45..ed9f490a00 100644
--- a/src/OFS/ObjectManager.py
+++ b/src/OFS/ObjectManager.py
@@ -769,8 +769,8 @@ def manage_FTPlist(self, REQUEST):
 
             files.sort()
 
-            if not hasattr(self, 'isTopLevelPrincipiaApplicationObject') and \
-               self.isTopLevelPrincipiaApplicationObject:
+            if not (hasattr(self, 'isTopLevelPrincipiaApplicationObject') and
+                    self.isTopLevelPrincipiaApplicationObject):
                 files.insert(0, ('..', aq_parent(self)))
             files.insert(0, ('.', self))
             for k, v in files: