diff --git a/polyglot/downloader.py b/polyglot/downloader.py
index bcc7a50..e5f4641 100644
--- a/polyglot/downloader.py
+++ b/polyglot/downloader.py
@@ -948,7 +948,7 @@ def get_collection(self, lang=None, task=None):
       if lang: raise LanguageNotSupported("Language {} is not supported".format(id))
       if task: raise TaskNotSupported("Task {} is not supported".format(id))
 
-  def supported_language(lang):
+  def supported_language(self, lang):
     """Return True if polyglot supports the language.
 
     Args: