diff --git a/pytorch_lightning/utilities/argparse_utils.py b/pytorch_lightning/utilities/argparse_utils.py
index 80db2429f7..17f0e9b8cc 100644
--- a/pytorch_lightning/utilities/argparse_utils.py
+++ b/pytorch_lightning/utilities/argparse_utils.py
@@ -3,3 +3,7 @@ from pytorch_lightning.utilities import rank_zero_deprecation
 rank_zero_deprecation("`argparse_utils` package has been renamed to `argparse` since v1.2 and will be removed in v1.4")
 
 from pytorch_lightning.utilities.argparse import *  # noqa: F403 E402 F401
+
+# for backward compatibility with old checkpoints (versions < 1.2.0)
+# that need to be able to unpickle the function from the checkpoint
+from pytorch_lightning.utilities.argparse import _gpus_arg_default  # noqa: E402 F401 # isort: skip