diff --git a/pkgs/development/python-modules/hypercorn/default.nix b/pkgs/development/python-modules/hypercorn/default.nix
index dc165f2b2cc4..35a9f8f6bb85 100644
--- a/pkgs/development/python-modules/hypercorn/default.nix
+++ b/pkgs/development/python-modules/hypercorn/default.nix
@@ -44,6 +44,10 @@ buildPythonPackage rec {
     pytestCheckHook
   ] ++ lib.optionals (pythonOlder "3.8") [ mock ];
 
+  pytestFlagsArray = [
+    "--asyncio-mode=legacy"
+  ];
+
   pythonImportsCheck = [ "hypercorn" ];
 
   meta = with lib; {