diff --git a/samcli/lib/bootstrap/companion_stack/companion_stack_manager.py b/samcli/lib/bootstrap/companion_stack/companion_stack_manager.py
index 4a531de679..8f183beb40 100644
--- a/samcli/lib/bootstrap/companion_stack/companion_stack_manager.py
+++ b/samcli/lib/bootstrap/companion_stack/companion_stack_manager.py
@@ -64,7 +64,7 @@ def __init__(self, stack_name, region, s3_bucket, s3_prefix):
         except NoRegionError as ex:
             raise RegionError(
                 "Error Setting Up Managed Stack Client: Unable to resolve a region. "
-                "Please provide a region via the --region parameter or by the AWS_REGION environment variable."
+                "Please provide a region via the --region parameter or by the AWS_DEFAULT_REGION environment variable."
             ) from ex
 
     def set_functions(
diff --git a/samcli/lib/utils/managed_cloudformation_stack.py b/samcli/lib/utils/managed_cloudformation_stack.py
index 3528e97c20..83cee2e0a5 100644
--- a/samcli/lib/utils/managed_cloudformation_stack.py
+++ b/samcli/lib/utils/managed_cloudformation_stack.py
@@ -84,7 +84,7 @@ def update_stack(
     except NoRegionError as ex:
         raise RegionError(
             "Error Setting Up Managed Stack Client: Unable to resolve a region. "
-            "Please provide a region via the --region parameter or by the AWS_REGION environment variable."
+            "Please provide a region via the --region parameter or by the AWS_DEFAULT_REGION environment variable."
         ) from ex
     return _create_or_update_stack(cloudformation_client, stack_name, template_body, parameter_overrides)
 
@@ -140,7 +140,7 @@ def manage_stack(
     except NoRegionError as ex:
         raise RegionError(
             "Error Setting Up Managed Stack Client: Unable to resolve a region. "
-            "Please provide a region via the --region parameter or by the AWS_REGION environment variable."
+            "Please provide a region via the --region parameter or by the AWS_DEFAULT_REGION environment variable."
         ) from ex
     return _create_or_get_stack(cloudformation_client, stack_name, template_body, parameter_overrides)