diff --git a/calendarweek/util.py b/calendarweek/util.py
index 466b9508cff44b9d1588d41264a714c8089fdaa9..913c0f494dd50662c99425e8aac76493e131a033 100644
--- a/calendarweek/util.py
+++ b/calendarweek/util.py
@@ -3,7 +3,7 @@ from typing import Optional
 
 
 def normalise_locale(loc: str, enc: Optional[str] = None) -> str:
-    loc = locale_alias.get(loc, loc)
+    loc = locale_alias.get(loc, loc) or ""
     if loc:
         if enc:
             enc = locale_encoding_alias.get(enc.replace("-", ""), enc)