diff --git a/sphinxtools/librarydescription.py b/sphinxtools/librarydescription.py
index e44807a5..3c84484e 100644
--- a/sphinxtools/librarydescription.py
+++ b/sphinxtools/librarydescription.py
@@ -526,7 +526,7 @@ class Library(ParentBase):
         class_dict = {}
         class_dict = self.ClassesToPickle(self, class_dict)
 
-        pickle_file = os.path.join(SPHINXROOT, 'class_summary.lst')
+        pickle_file = os.path.join(SPHINXROOT, 'class_summary.pkl')
         with PickleFile(pickle_file) as pf:
             pf.items.update(class_dict)
 
diff --git a/sphinxtools/modulehunter.py b/sphinxtools/modulehunter.py
index 0ecb1805..c571d76c 100644
--- a/sphinxtools/modulehunter.py
+++ b/sphinxtools/modulehunter.py
@@ -585,7 +585,7 @@ def ToRest(import_name):
     pf = PickleFile(pickle_file)
     library_class = pf.read()
 
-    pf = PickleFile(os.path.join(sphinxDir, 'class_summary.lst'))
+    pf = PickleFile(os.path.join(sphinxDir, 'class_summary.pkl'))
     class_summary = pf.read()
 
     library_class.Walk(library_class, class_summary)
diff --git a/sphinxtools/postprocess.py b/sphinxtools/postprocess.py
index 4351770b..79966c44 100644
--- a/sphinxtools/postprocess.py
+++ b/sphinxtools/postprocess.py
@@ -96,7 +96,7 @@ def buildEnumsAndMethods(sphinxDir):
     4. Some cleanup.
     """
 
-    pf = PickleFile(os.path.join(sphinxDir, 'class_summary.lst'))
+    pf = PickleFile(os.path.join(sphinxDir, 'class_summary.pkl'))
     class_summary = pf.read()
     
     unreferenced_classes = {}
diff --git a/sphinxtools/utilities.py b/sphinxtools/utilities.py
index ea5601a2..6474eb9a 100644
--- a/sphinxtools/utilities.py
+++ b/sphinxtools/utilities.py
@@ -687,7 +687,7 @@ def pickleClassInfo(class_name, element, short_description):
     for base in element.bases:
         bases.append(wx2Sphinx(base)[1])
 
-    pickle_file = os.path.join(SPHINXROOT, 'class_summary.lst')
+    pickle_file = os.path.join(SPHINXROOT, 'class_summary.pkl')
     with PickleFile(pickle_file) as pf:
         pf.items[class_name] = (method_list, bases, short_description)