diff --git a/pwiki/wiki.py b/pwiki/wiki.py
index 4fcc993..1239858 100644
--- a/pwiki/wiki.py
+++ b/pwiki/wiki.py
@@ -51,8 +51,8 @@ def __init__(self, domain: str = "en.wikipedia.org", username: str = None, passw
 
         self._refresh_rights()
 
-        if not self._load_cookies(username):
-            self.login(username, password)
+        if username and not (self._load_cookies(username) or self.login(username, password)):
+            raise RuntimeError(f"Failed to login for '{username}'!")
 
         self.ns_manager: NSManager = OQuery.fetch_namespaces(self)