diff --git a/pytorch_lightning/trainer/trainer.py b/pytorch_lightning/trainer/trainer.py
index 9b27655675dc9..304d50800fcec 100644
--- a/pytorch_lightning/trainer/trainer.py
+++ b/pytorch_lightning/trainer/trainer.py
@@ -667,6 +667,16 @@ def add_argparse_args(cls, parent_parser: ArgumentParser) -> ArgumentParser:
                     def allowed_type(x):
                         return bool(parsing.strtobool(x))
 
+                    # Bool args with default of True parsed as flags not key value pair
+                    if arg_types == (bool,) and arg_default is False:
+                        parser.add_argument(
+                            f'--{arg}',
+                            action='store_true',
+                            dest=arg,
+                            help='autogenerated by pl.Trainer'
+                        )
+                        continue
+
                 if arg == 'gpus':
                     allowed_type = Trainer.allowed_type
                     arg_default = Trainer.arg_default
diff --git a/tests/trainer/test_trainer_cli.py b/tests/trainer/test_trainer_cli.py
index fdc78d43fe288..9b0e64dfefb7a 100644
--- a/tests/trainer/test_trainer_cli.py
+++ b/tests/trainer/test_trainer_cli.py
@@ -30,7 +30,7 @@ def test_default_args(tmpdir):
 
 @pytest.mark.parametrize('cli_args', [
     ['--accumulate_grad_batches=22'],
-    ['--print_nan_grads=1', '--weights_save_path=./'],
+    ['--print_nan_grads', '--weights_save_path=./'],
     []
 ])
 def test_add_argparse_args_redefined(cli_args):