diff --git a/nominatim/tokenizer/icu_tokenizer.py b/nominatim/tokenizer/icu_tokenizer.py
index 28184f6a..df1387e2 100644
--- a/nominatim/tokenizer/icu_tokenizer.py
+++ b/nominatim/tokenizer/icu_tokenizer.py
@@ -624,7 +624,7 @@ class LegacyICUNameAnalyzer(AbstractAnalyzer):
         if postcode not in self._cache.postcodes:
             term = self._search_normalized(postcode_name)
             if not term:
-                return
+                return None
 
             variants = {term}
             if analyzer is not None and variant_base is not None: