diff --git a/joblib/test/test_parallel.py b/joblib/test/test_parallel.py
index e15c9955c..8d7673951 100644
--- a/joblib/test/test_parallel.py
+++ b/joblib/test/test_parallel.py
@@ -1032,6 +1032,7 @@ def test_parallel_with_unpicklable_functions_in_args(
 
 INTERACTIVE_DEFINED_FUNCTION_AND_CLASS_SCRIPT_CONTENT = """\
 import sys
+import faulthandler
 # Make sure that joblib is importable in the subprocess launching this
 # script. This is needed in case we run the tests from the joblib root
 # folder without having installed joblib
@@ -1056,6 +1057,9 @@ def square(x, ignored=None, ignored2=None):
 # Here, we do not need the `if __name__ == "__main__":` safeguard when
 # using the default `loky` backend (even on Windows).
 
+# To make debugging easier
+faulthandler.dump_traceback_later(30, exit=True)
+
 # The following baroque function call is meant to check that joblib
 # introspection rightfully uses cloudpickle instead of the (faster) pickle
 # module of the standard library when necessary. In particular cloudpickle is
@@ -1078,9 +1082,11 @@ def test_parallel_with_interactively_defined_functions_default_backend(tmpdir):
     # filesystem script.
     script = tmpdir.join('joblib_interactively_defined_function.py')
     script.write(INTERACTIVE_DEFINED_FUNCTION_AND_CLASS_SCRIPT_CONTENT)
-    check_subprocess_call([sys.executable, script.strpath],
-                          stdout_regex=r'\[0, 1, 4, 9, 16\]',
-                          timeout=5)
+    check_subprocess_call(
+        [sys.executable, script.strpath],
+        stdout_regex=r'\[0, 1, 4, 9, 16\]',
+        timeout=None,  # rely on faulthandler to kill the process
+    )
 
 
 INTERACTIVELY_DEFINED_SUBCLASS_WITH_METHOD_SCRIPT_CONTENT = """\
diff --git a/joblib/testing.py b/joblib/testing.py
index 28f79311c..f8939f056 100644
--- a/joblib/testing.py
+++ b/joblib/testing.py
@@ -50,9 +50,10 @@ def kill_process():
         warnings.warn("Timeout running {}".format(cmd))
         proc.kill()
 
-    timer = threading.Timer(timeout, kill_process)
     try:
-        timer.start()
+        if timeout is not None:
+            timer = threading.Timer(timeout, kill_process)
+            timer.start()
         stdout, stderr = proc.communicate()
         stdout, stderr = stdout.decode(), stderr.decode()
         if proc.returncode != 0:
@@ -74,4 +75,5 @@ def kill_process():
                     stderr_regex, stderr))
 
     finally:
-        timer.cancel()
+        if timeout is not None:
+            timer.cancel()