diff --git a/backend/address2UPRN/main.py b/backend/address2UPRN/main.py
index 6b684cef..e49088f4 100644
--- a/backend/address2UPRN/main.py
+++ b/backend/address2UPRN/main.py
@@ -61,7 +61,7 @@ def get_uprn_from_historic_epc(
         return None
 
     uprn: Optional[str] = result.unambiguous_uprn()
-    if not uprn or uprn in ("", "nan"):
+    if not uprn or uprn == "nan":
         return None
 
     top = result.top()