diff --git a/src/calibre/utils/xml_parse.py b/src/calibre/utils/xml_parse.py
index d0228d5e3f..d53a787721 100644
--- a/src/calibre/utils/xml_parse.py
+++ b/src/calibre/utils/xml_parse.py
@@ -4,31 +4,28 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-
 from lxml import etree
 import threading
 
-
 # resolve_entities is turned off as entities can cause
 # reads of local files, for example:
 # <!DOCTYPE foo [ <!ENTITY passwd SYSTEM "file:///etc/passwd" >]>
 
-
-class GlobalParserTLS(threading.local):
-
-    def __call__(self, recover):
-        parsers = getattr(self, 'parsers', None)
-        if parsers is None:
-            self.parsers = parsers = {
-                True: etree.XMLParser(recover=True, no_network=True, resolve_entities=False),
-                False: etree.XMLParser(recover=False, no_network=True, resolve_entities=False)
-            }
-        return parsers[recover]
-
-
-_global_tls = GlobalParserTLS()
+_global_tls = threading.local()
 fs = etree.fromstring
 
 
+def parser(recover):
+    parsers = getattr(_global_tls, 'parsers', None)
+    if parsers is None:
+        _global_tls.parsers = parsers = {
+            True:
+            etree.XMLParser(recover=True, no_network=True, resolve_entities=False),
+            False:
+            etree.XMLParser(recover=False, no_network=True, resolve_entities=False)
+        }
+        return parsers[recover]
+
+
 def safe_xml_fromstring(string_or_bytes, recover=True):
-    return fs(string_or_bytes, _global_tls(recover))
+    return fs(string_or_bytes, parser(recover))