diff --git a/tests/test_runner/test_parallel.py b/tests/test_runner/test_parallel.py
index fa129da768..32cc971d30 100644
--- a/tests/test_runner/test_parallel.py
+++ b/tests/test_runner/test_parallel.py
@@ -32,6 +32,12 @@ class ExceptionThatFailsUnpickling(Exception):
     def __init__(self, arg):
         super().__init__()
 
+    def __reduce__(self):
+        # tblib 3.2+ makes exception subclasses picklable by default.
+        # Return (cls, ()) so the constructor fails on unpickle, preserving
+        # the needed behavior for test_pickle_errors_detection.
+        return (self.__class__, ())
+
 
 class ParallelTestRunnerTest(SimpleTestCase):
     """
@@ -170,6 +176,8 @@ class RemoteTestResultTest(SimpleTestCase):
         result = RemoteTestResult()
         result._confirm_picklable(picklable_error)
 
+        # The exception can be pickled but not unpickled.
+        pickle.dumps(not_unpicklable_error)
         msg = "__init__() missing 1 required positional argument"
         with self.assertRaisesMessage(TypeError, msg):
             result._confirm_picklable(not_unpicklable_error)