diff --git a/fix_tei.py b/fix_tei.py
index 1797f93..f537f37 100644
--- a/fix_tei.py
+++ b/fix_tei.py
@@ -361,7 +361,7 @@ def cleanup_xml(xml_tree):
     for attribute in xml_preserve:
         attribute.attrib.pop("{http://www.w3.org/XML/1998/namespace}space")
 
-    formulae = xmltree.xpath("//t:formula", namespaces=NS_MAP)
+    formulae = xml_tree.xpath("//t:formula", namespaces=NS_MAP)
     logging.info(f"Found {len(formulae)} formulae.")
 
     for formula in formulae: