diff --git a/src/calibre/ebooks/oeb/transforms/split.py b/src/calibre/ebooks/oeb/transforms/split.py
index 65fdb91698..24a77fe0e6 100644
--- a/src/calibre/ebooks/oeb/transforms/split.py
+++ b/src/calibre/ebooks/oeb/transforms/split.py
@@ -76,7 +76,7 @@ class Split(object):
         if splitter.was_split:
             am = splitter.anchor_map
             self.map[item.href] = collections.defaultdict(
-                    am.default_factory, **am)
+                    am.default_factory, am)
 
     def find_page_breaks(self, item):
         if self.page_break_selectors is None: