diff --git a/dlibrary/dlibrary.py b/dlibrary/dlibrary.py
index 223ed45..45cb376 100755
--- a/dlibrary/dlibrary.py
+++ b/dlibrary/dlibrary.py
@@ -869,7 +869,7 @@ def unique_hierarchical_prefix_numbering(entries, start_point=0):
     for m in matches:
         pos = m.start()
         if pos < start_point:
-            return None
+            break
         prefix = nname(longest_entry)[:pos]
         debug(f'Checking prefix {prefix}')
         if all(nname(e).startswith(prefix) or prefix.startswith(nfc(e.stem)) for e in entries):