diff --git a/zkapauthorizer.nix b/zkapauthorizer.nix
index 77bbf6657c479b9daab7c133286c0c626efdb104..1a352e4285283753b614732062be8777706e1cf6 100644
--- a/zkapauthorizer.nix
+++ b/zkapauthorizer.nix
@@ -4,12 +4,12 @@
 , hypothesisProfile ? null
 , collectCoverage ? false
 , testSuite ? null
-, trialArgs ? []
+, trialArgs ? null
 }:
 let
   hypothesisProfile' = if hypothesisProfile == null then "default" else hypothesisProfile;
   testSuite' = if testSuite == null then "_zkapauthorizer" else testSuite;
-  extraTrialArgs = builtins.concatStringsSep " " trialArgs;
+  extraTrialArgs = builtins.concatStringsSep " " (if trialArgs == null then ["--rterrors" "--jobs=4" ] else trialArgs);
 in
 buildPythonPackage rec {
   version = "0.0";