diff --git a/tests/conftest.py b/tests/conftest.py
index 90357e0..9b5abf1 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -4,6 +4,11 @@ Sets dummy environment variables at import time so modules that read
 ``os.environ`` at module load (slackio, interactions, handler) can be imported
 without real AWS credentials.  Real values are monkeypatched per-test where
 needed.
+
+A default AWS region is set too: the handler/slackio modules construct
+``boto3.client(...)`` at import time, which raises ``NoRegionError`` on a CI
+runner with no AWS config. Client construction is offline; every real AWS call
+is monkeypatched in the tests.
 """
 
 import os
@@ -11,3 +16,5 @@ import os
 os.environ.setdefault("SLACK_SECRET_NAME", "test-slack-secret")
 os.environ.setdefault("DASHBOARD_URL_PARAM", "/test/dashboard-url")
 os.environ.setdefault("ANALYTICS_BUCKET", "test-bucket")
+os.environ.setdefault("AWS_DEFAULT_REGION", "us-east-1")
+os.environ.setdefault("AWS_REGION", "us-east-1")