diff --git a/docker/Dockerfile b/docker/Dockerfile
index 058227f7..d29c6a7b 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -9,3 +9,4 @@ RUN apk --update add --virtual build-dependencies python3-dev build-base \
   && apk del build-dependencies
 
 ENTRYPOINT ["pymap"]
+CMD ["--help"]
diff --git a/pymap/config.py b/pymap/config.py
index 8ef26c03..9eec9450 100644
--- a/pymap/config.py
+++ b/pymap/config.py
@@ -203,8 +203,14 @@ def _get_cpu_subsystem(cls) -> Subsystem:
 
     @classmethod
     def _load_certs(cls, extra: Mapping[str, Any]) -> SSLContext:
-        cert_file: Optional[str] = extra.get('cert_file')
-        key_file: Optional[str] = extra.get('key_file')
+        try:
+            cert_file: Optional[str] = os.environ['CERT_FILE']
+        except KeyError:
+            cert_file = extra.get('cert_file')
+        try:
+            key_file: Optional[str] = os.environ['KEY_FILE']
+        except KeyError:
+            key_file = extra.get('key_file')
         ssl_context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
         if cert_file is not None:
             ssl_context.load_cert_chain(cert_file, key_file)
diff --git a/setup.py b/setup.py
index fb5e82af..da9281c2 100644
--- a/setup.py
+++ b/setup.py
@@ -28,7 +28,7 @@
     license = f.read()
 
 setup(name='pymap',
-      version='0.20.2',
+      version='0.20.3',
       author='Ian Good',
       author_email='ian@icgood.net',
       description='Lightweight, asynchronous IMAP serving in Python.',