From 2e6b40cb1b7fd18ee945fd3cac517a281b67b05d Mon Sep 17 00:00:00 2001
From: Alex Lindsay <alexlindsay239@gmail.com>
Date: Wed, 23 May 2018 14:16:17 -0600
Subject: [PATCH] Consistently check derived for sum and sum_sq in tallies.
 Closes #1010

---
 openmc/tallies.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/openmc/tallies.py b/openmc/tallies.py
index a5341cbedd..74f3429034 100644
--- a/openmc/tallies.py
+++ b/openmc/tallies.py
@@ -248,7 +248,7 @@ class Tally(IDManagerMixin):
 
     @property
     def sum_sq(self):
-        if not self._sp_filename:
+        if not self._sp_filename or self.derived:
             return None
 
         if not self._results_read: