diff --git a/Dockerfile b/Dockerfile
index 7072ecb..38d718e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,5 @@
 FROM python:3.8-slim-buster
+LABEL org.opencontainers.image.source https://github.com/github/stale_repos
 
 WORKDIR /action/workspace
 COPY requirements.txt stale_repos.py /action/workspace/
diff --git a/requirements.txt b/requirements.txt
index afd6006..bb78d4a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,3 @@
 github3.py==4.0.1
 python-dotenv==1.0.0
+python_dateutil==2.8.2
diff --git a/stale_repos.py b/stale_repos.py
index 11c15d1..cc07420 100755
--- a/stale_repos.py
+++ b/stale_repos.py
@@ -1,10 +1,12 @@
 #!/usr/bin/env python
+""" Find stale repositories in a GitHub organization. """
 
 import os
 from datetime import datetime
 from os.path import dirname, join
 
 import github3
+from dateutil.parser import parse
 from dotenv import load_dotenv
 
 
@@ -31,12 +33,15 @@ def main():
     ghe = os.getenv("GH_ENTERPRISE_URL", default="").strip()
     token = os.getenv("GH_TOKEN")
     if ghe and token:
-        gh = github3.github.GitHubEnterprise(ghe, token=token)
+        github_connection = github3.github.GitHubEnterprise(ghe, token=token)
     elif token:
-        gh = github3.login(token=os.getenv("GH_TOKEN"))
+        github_connection = github3.login(token=os.getenv("GH_TOKEN"))
     else:
         raise ValueError("GH_TOKEN environment variable not set")
 
+    if not github_connection:
+        raise ValueError("Unable to authenticate to GitHub")
+
     # Set the threshold for inactive days
     inactive_days_threshold = os.getenv("INACTIVE_DAYS")
     if not inactive_days_threshold:
@@ -49,14 +54,14 @@ def main():
 
     # Iterate over repos in the org, acquire inactive days,
     # and print out the repo url and days inactive if it's over the threshold (inactive_days)
-    for repo in gh.repositories_by(organization):
-        last_push_str = repo.pushed_at
+    for repo in github_connection.repositories_by(organization):
+        last_push_str = repo.pushed_at  # type: ignore
         if last_push_str is None:
             continue
-        last_push = datetime.fromisoformat(last_push_str[:-1])
+        last_push = parse(last_push_str)
         days_inactive = (datetime.now() - last_push).days
         if days_inactive > int(inactive_days_threshold):
-            print(f"{repo.html_url}: {days_inactive} days inactive")
+            print(f"{repo.html_url}: {days_inactive} days inactive")  # type: ignore
 
 
 if __name__ == "__main__":