diff --git a/crosspoint_reader/textsplit.py b/crosspoint_reader/textsplit.py
index 67b9e95..aa773fa 100644
--- a/crosspoint_reader/textsplit.py
+++ b/crosspoint_reader/textsplit.py
@@ -400,7 +400,7 @@ def _split_epub_text(path, log, result, profile=None, opts=None):
             if k > 0:
                 order.insert(insert_at + k, new_zname)
             for frag in re.findall(r'id="([^"]+)"', content):
-                anchor_map[(posixpath.basename(href), frag)] = name
+                anchor_map.setdefault((posixpath.basename(href), frag), name)
 
         new_items = []
         new_refs = []