diff --git a/django/test/runner.py b/django/test/runner.py
index f2a91373b1..6bcf4111df 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -398,6 +398,7 @@ def _init_worker(
     serialized_contents=None,
     process_setup=None,
     process_setup_args=None,
+    debug_mode=None,
 ):
     """
     Switch to databases dedicated to this worker.
@@ -420,7 +421,7 @@ def _init_worker(
                 process_setup_args = ()
             process_setup(*process_setup_args)
         django.setup()
-        setup_test_environment()
+        setup_test_environment(debug=debug_mode)
 
     for alias in connections:
         connection = connections[alias]
@@ -473,10 +474,13 @@ class ParallelTestSuite(unittest.TestSuite):
     run_subsuite = _run_subsuite
     runner_class = RemoteTestRunner
 
-    def __init__(self, subsuites, processes, failfast=False, buffer=False):
+    def __init__(
+        self, subsuites, processes, failfast=False, debug_mode=False, buffer=False
+    ):
         self.subsuites = subsuites
         self.processes = processes
         self.failfast = failfast
+        self.debug_mode = debug_mode
         self.buffer = buffer
         self.initial_settings = None
         self.serialized_contents = None
@@ -508,6 +512,7 @@ class ParallelTestSuite(unittest.TestSuite):
                 self.serialized_contents,
                 self.process_setup.__func__,
                 self.process_setup_args,
+                self.debug_mode,
             ],
         )
         args = [
@@ -933,6 +938,7 @@ class DiscoverRunner:
                     subsuites,
                     processes,
                     self.failfast,
+                    self.debug_mode,
                     self.buffer,
                 )
         return suite
diff --git a/docs/releases/4.1.2.txt b/docs/releases/4.1.2.txt
index 47b53f0e8b..434bc5f587 100644
--- a/docs/releases/4.1.2.txt
+++ b/docs/releases/4.1.2.txt
@@ -31,3 +31,7 @@ Bugfixes
 * Fixed a regression in Django 4.1 where the app registry was not populated
   when running parallel tests with the ``multiprocessing`` start method
   ``spawn`` (:ticket:`34010`).
+
+* Fixed a regression in Django 4.1 where the ``--debug-mode`` argument to
+  ``test`` did not work when running parallel tests with the
+  ``multiprocessing`` start method ``spawn`` (:ticket:`34010`).
diff --git a/tests/test_runner/tests.py b/tests/test_runner/tests.py
index b3c7cc5a55..30ea4ea670 100644
--- a/tests/test_runner/tests.py
+++ b/tests/test_runner/tests.py
@@ -713,7 +713,9 @@ class TestRunnerInitializerTests(SimpleTestCase):
                 runner = self.test_runner(**kwargs)
                 return runner.run(suite)
 
-        runner = StubTestRunner(verbosity=0, interactive=False, parallel=2)
+        runner = StubTestRunner(
+            verbosity=0, interactive=False, parallel=2, debug_mode=True
+        )
         with self.assertRaisesMessage(Exception, "multiprocessing.Pool()"):
             runner.run_tests(
                 [
@@ -723,6 +725,9 @@ class TestRunnerInitializerTests(SimpleTestCase):
             )
         # Initializer must be a function.
         self.assertIs(mocked_pool.call_args.kwargs["initializer"], _init_worker)
+        initargs = mocked_pool.call_args.kwargs["initargs"]
+        self.assertEqual(len(initargs), 6)
+        self.assertEqual(initargs[5], True)  # debug_mode
 
 
 class Ticket17477RegressionTests(AdminScriptTestCase):