diff --git a/pytorch_lightning/utilities/migration.py b/pytorch_lightning/utilities/migration.py
index bc3761e47b835..30cc823210423 100644
--- a/pytorch_lightning/utilities/migration.py
+++ b/pytorch_lightning/utilities/migration.py
@@ -14,10 +14,14 @@
 from __future__ import annotations
 
 import sys
+import threading
 from types import ModuleType, TracebackType
 
 import pytorch_lightning.utilities.argparse
 
+# Create a global lock to ensure no race condition with deleting sys modules
+_lock = threading.Lock()
+
 
 class pl_legacy_patch:
     """Registers legacy artifacts (classes, methods, etc.) that were removed but still need to be included for
@@ -35,6 +39,7 @@ class pl_legacy_patch:
     """
 
     def __enter__(self) -> None:
+        _lock.acquire()
         # `pl.utilities.argparse_utils` was renamed to `pl.utilities.argparse`
         legacy_argparse_module = ModuleType("pytorch_lightning.utilities.argparse_utils")
         sys.modules["pytorch_lightning.utilities.argparse_utils"] = legacy_argparse_module
@@ -49,3 +54,4 @@ def __exit__(
         if hasattr(pytorch_lightning.utilities.argparse, "_gpus_arg_default"):
             delattr(pytorch_lightning.utilities.argparse, "_gpus_arg_default")
         del sys.modules["pytorch_lightning.utilities.argparse_utils"]
+        _lock.release()
diff --git a/tests/checkpointing/test_legacy_checkpoints.py b/tests/checkpointing/test_legacy_checkpoints.py
index 7e753617a6331..ac2806cbf3811 100644
--- a/tests/checkpointing/test_legacy_checkpoints.py
+++ b/tests/checkpointing/test_legacy_checkpoints.py
@@ -14,6 +14,7 @@
 import glob
 import os
 import sys
+import threading
 from unittest.mock import patch
 
 import pytest
@@ -60,6 +61,28 @@ def on_train_epoch_start(self, trainer: "pl.Trainer", pl_module: "pl.LightningMo
             trainer.should_stop = True
 
 
+@pytest.mark.parametrize("pl_version", LEGACY_BACK_COMPATIBLE_PL_VERSIONS)
+def test_legacy_ckpt_threading(tmpdir, pl_version: str):
+    def load_model():
+        import torch
+
+        from pytorch_lightning.utilities.migration import pl_legacy_patch
+
+        with pl_legacy_patch():
+            _ = torch.load(PATH_LEGACY)
+
+    PATH_LEGACY = os.path.join(LEGACY_CHECKPOINTS_PATH, pl_version)
+    with patch("sys.path", [PATH_LEGACY] + sys.path):
+        t1 = threading.Thread(target=load_model)
+        t2 = threading.Thread(target=load_model)
+
+        t1.start()
+        t2.start()
+
+        t1.join()
+        t2.join()
+
+
 @pytest.mark.parametrize("pl_version", LEGACY_BACK_COMPATIBLE_PL_VERSIONS)
 def test_resume_legacy_checkpoints(tmpdir, pl_version: str):
     PATH_LEGACY = os.path.join(LEGACY_CHECKPOINTS_PATH, pl_version)