diff --git a/Dockerfile b/Dockerfile
index 35fef53f..59d42084 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -33,6 +33,7 @@ RUN pip install --no-cache-dir /deps/*.whl
 
 COPY --from=builder /doccano /doccano
 
+ENV IS_HEROKU="False"
 ENV DEBUG="True"
 ENV SECRET_KEY="change-me-in-production"
 ENV PORT="80"
diff --git a/app/app/settings.py b/app/app/settings.py
index 730c0b78..c4e804d4 100644
--- a/app/app/settings.py
+++ b/app/app/settings.py
@@ -219,7 +219,9 @@ APPLICATION_INSIGHTS = {
     'ikey': AZURE_APPINSIGHTS_IKEY if AZURE_APPINSIGHTS_IKEY else None,
 }
 
-django_heroku.settings(locals(), test_runner=False)
+# work-around for django-heroku: don't overwrite sslmode outside of heroku
+if env.bool('IS_HEROKU', True):
+    django_heroku.settings(locals(), test_runner=False)
 
 # work-around for dj-database-url: explicitly disable ssl for sqlite
 if DATABASES['default'].get('ENGINE') == 'django.db.backends.sqlite3':