diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 145f897..a6079be 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -835,7 +835,7 @@ def authenticate(user, secret, authtype = DEFAULT_AUTH_TYPE)
       check_auth_method authtype
       check_auth_args user, secret
       authenticator = Authenticator.auth_class(authtype).new(self)
-      authenticator.auth(user, secret)
+      critical { authenticator.auth(user, secret) }
     end
 
     private