diff --git a/yawsso/cli.py b/yawsso/cli.py
index 4b2195e..db41fad 100644
--- a/yawsso/cli.py
+++ b/yawsso/cli.py
@@ -36,6 +36,9 @@ def boot():
     if args.bin:
         core.aws_bin = args.bin
 
+    if args.region:
+        core.region_flag = args.region
+
     logger.log(TRACE, f"args: {args}")
     logger.log(TRACE, f"AWS_CONFIG_FILE: {core.aws_config_file}")
     logger.log(TRACE, f"AWS_SHARED_CREDENTIALS_FILE: {core.aws_shared_credentials_file}")
@@ -60,6 +63,7 @@ def parser():
     ap.add_argument("-t", "--trace", help="Trace output", action="store_true")
     ap.add_argument("-e", "--export-vars", dest="export_vars1", help="Print out AWS ENV vars", action="store_true")
     ap.add_argument("-v", "--version", help="Print version and exit", action="store_true")
+    ap.add_argument("-r", "--region", help="Add region to credentials file", action="store_true")
 
     sp = ap.add_subparsers(title="available commands", metavar="", dest="command")
 
diff --git a/yawsso/core.py b/yawsso/core.py
index e9ca448..d80c39f 100644
--- a/yawsso/core.py
+++ b/yawsso/core.py
@@ -11,7 +11,8 @@ profiles = None
 aws_sso_cache_path = u.xu(os.getenv("AWS_SSO_CACHE_PATH", Constant.AWS_SSO_CACHE_PATH.value))
 aws_config_file = u.xu(os.getenv("AWS_CONFIG_FILE", Constant.AWS_CONFIG_FILE.value))
 aws_shared_credentials_file = u.xu(os.getenv("AWS_SHARED_CREDENTIALS_FILE", Constant.AWS_SHARED_CREDENTIALS_FILE.value))
-aws_default_region = os.getenv("AWS_DEFAULT_REGION", Constant.AWS_DEFAULT_REGION.value)
+aws_default_region = os.getenv("AWS_DEFAULT_REGION")
+region_flag = False  # See https://github.com/victorskl/yawsso/issues/76
 
 
 def get_aws_cli_v2_sso_cached_login(profile):
@@ -34,19 +35,29 @@ def update_aws_cli_v1_credentials(profile_name, profile, credentials):
         logger.warning(f"No appropriate credentials found. Skip syncing profile `{profile_name}`")
         return
 
-    # region = profile.get("region", aws_default_region)
     config = u.read_config(aws_shared_credentials_file)
+
     if config.has_section(profile_name):
         config.remove_section(profile_name)
+
     config.add_section(profile_name)
-    # config.set(profile_name, "region", region)  # See https://github.com/victorskl/yawsso/issues/76
     config.set(profile_name, "aws_access_key_id", credentials["accessKeyId"])
     config.set(profile_name, "aws_secret_access_key", credentials["secretAccessKey"])
     config.set(profile_name, "aws_session_token", credentials["sessionToken"])
     config.set(profile_name, "aws_security_token", credentials["sessionToken"])
+
+    # set expiration
     ts_expires_millisecond = credentials["expiration"]
     dt_utc = str(datetime.utcfromtimestamp(ts_expires_millisecond / 1000.0).isoformat() + '+0000')
     config.set(profile_name, "aws_session_expiration", dt_utc)
+
+    # set region
+    region = profile.get("region", aws_default_region)
+    if region_flag and region:
+        # See https://github.com/victorskl/yawsso/issues/88
+        config.set(profile_name, "region", region)
+
+    # write the config out
     u.write_config(aws_shared_credentials_file, config)
 
     logger.debug(f"Done syncing AWS CLI v1 credentials using AWS CLI v2 SSO login session for profile `{profile_name}`")

diff --git a/tests/test_cli.py b/tests/test_cli.py
index 58ad488..e246da3 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -1056,3 +1056,16 @@ class CLIUnitTests(TestCase):
         self.assertNotEqual(new_tok, 'tok')
         self.assertEqual(new_tok, 'VeryLongBase664String==')
         verify(cli.utils, times=1).Poll(...)
+
+    def test_region_flag(self):
+        """
+        python -m unittest tests.test_cli.CLIUnitTests.test_region_flag
+        """
+        with ArgvContext(program, '-p', 'dev', '-t', '-r'):
+            cli.main()
+            cred = cli.utils.read_config(self.credentials.name)
+            new_tok = cred['dev']['aws_session_token']
+            self.assertNotEqual(new_tok, 'tok')
+            self.assertEqual(new_tok, 'VeryLongBase664String==')
+            self.assertEqual(cred['dev']['region'], 'ap-southeast-2')
+            verify(cli.utils, times=2).invoke(...)

Add parameter to control setting the region in the .aws/credentials file
Hi @victorskl,

I came across the issue reported in https://github.com/victorskl/yawsso/issues/76 because I was wondering why the aws clients are telling me that there is no default region defined in the profile. It has been working before, but then since I updated yawsso I started to have an issue. So actually my request would be the opposite as what is explained in https://github.com/victorskl/yawsso/issues/76. Do you think it would be possible to implement a parameter so that you can define whether you want the region in the credentials file or not? Something like a switch "-r" to tell it to copy the region for example?
yawsso -p dev:foo -r
[
tests/test_cli.py::CLIUnitTests::test_invalid_bin tests/test_cli.py::CLIUnitTests::test_invoke_cmd_fail tests/test_cli.py::CLIUnitTests::test_fetch_credentials_with_assume_role_no_success tests/test_cli.py::CLIUnitTests::test_no_such_profile_section tests/test_cli.py::CLIUnitTests::test_poll_cmd_fail tests/test_cli.py::CLIUnitTests::test_unknown_command tests/test_cli.py::CLIUnitTests::test_credential_not_found_2 tests/test_cli.py::CLIUnitTests::test_load_json_value_error tests/test_cli.py::CLIUnitTests::test_sso_cache_not_found tests/test_cli.py::CLIUnitTests::test_aws_cli_version_fail tests/test_cli.py::CLIUnitTests::test_poll_cmd_success tests/test_cli.py::CLIUnitTests::test_config_not_found tests/test_cli.py::CLIUnitTests::test_append_cli_global_options tests/test_cli.py::CLIUnitTests::test_version_flag tests/test_cli.py::CLIUnitTests::test_get_role_max_session_duration_no_success tests/test_cli.py::CLIUnitTests::test_aws_cli_v1 tests/test_cli.py::CLIUnitTests::test_eager_sync_source_profile_should_skip tests/test_cli.py::CLIUnitTests::test_xu tests/test_cli.py::CLIUnitTests::test_sso_get_role_credentials_fail tests/test_cli.py::CLIUnitTests::test_parse_credentials_file_session_expiry