diff --git a/requests/sessions.py b/requests/sessions.py
index db913089..8c06448e 100644
--- a/requests/sessions.py
+++ b/requests/sessions.py
@@ -704,7 +704,7 @@ class Session(SessionRedirectMixin):
     def mount(self, prefix, adapter):
         """Registers a connection adapter to a prefix.
 
-        Adapters are sorted in descending order by key length.
+        Adapters are sorted in descending order by prefix length.
         """
         self.adapters[prefix] = adapter
         keys_to_move = [k for k in self.adapters if len(k) < len(prefix)]