--- a/cmd/madon.go	Sun Apr 23 18:18:51 2017 +0200
+++ b/cmd/madon.go	Sun Apr 23 18:50:09 2017 +0200
@@ -94,6 +94,9 @@
 	if err == nil {
 		return nil
 	}
+	if !verbose && err.Error() == "cannot unmarshal server response: invalid character '<' looking for beginning of value" {
+		return fmt.Errorf("login failed (server did not return a JSON response - check your credentials)")
+	}
 	return fmt.Errorf("login failed: %s", err.Error())
 }