diff --git a/openmc/universe.py b/openmc/universe.py
index ccd0cb27c3..237ddce1f7 100644
--- a/openmc/universe.py
+++ b/openmc/universe.py
@@ -397,28 +397,28 @@ class Cell(object):
 
     def create_xml_subelement(self, xml_element):
         element = ET.Element("cell")
-        element.set("id", str(self._id))
+        element.set("id", str(self.id))
 
         if len(self._name) > 0:
-            element.set("name", str(self._name))
+            element.set("name", str(self.name))
 
-        if isinstance(self._fill, openmc.Material):
-            element.set("material", str(self._fill._id))
+        if isinstance(self.fill, basestring):
+            element.set("material", "void")
 
-        elif isinstance(self._fill, Iterable):
+        elif isinstance(self.fill, openmc.Material):
+            element.set("material", str(self.fill.id))
+
+        elif isinstance(self.fill, Iterable):
             element.set("material", ' '.join([m if m == 'void' else str(m.id)
                                               for m in self.fill]))
 
-        elif isinstance(self._fill, (Universe, Lattice)):
-            element.set("fill", str(self._fill._id))
-            self._fill.create_xml_subelement(xml_element)
-
-        elif self._fill.strip().lower() == "void":
-            element.set("material", "void")
+        elif isinstance(self.fill, (Universe, Lattice)):
+            element.set("fill", str(self.fill.id))
+            self.fill.create_xml_subelement(xml_element)
 
         else:
-            element.set("fill", str(self._fill))
-            self._fill.create_xml_subelement(xml_element)
+            element.set("fill", str(self.fill))
+            self.fill.create_xml_subelement(xml_element)
 
         if self.region is not None:
             # Set the region attribute with the region specification
@@ -445,11 +445,11 @@ class Cell(object):
             # Call the recursive function from the top node
             create_surface_elements(self.region, xml_element)
 
-        if self._translation is not None:
-            element.set("translation", ' '.join(map(str, self._translation)))
+        if self.translation is not None:
+            element.set("translation", ' '.join(map(str, self.translation)))
 
-        if self._rotation is not None:
-            element.set("rotation", ' '.join(map(str, self._rotation)))
+        if self.rotation is not None:
+            element.set("rotation", ' '.join(map(str, self.rotation)))
 
         return element