diff --git a/morss/wsgi.py b/morss/wsgi.py
index 2a3d422..d08385e 100644
--- a/morss/wsgi.py
+++ b/morss/wsgi.py
@@ -291,5 +291,5 @@ def cgi_start_server():
     httpd.serve_forever()
 
 
-if "gunicorn" in os.getenv('SERVER_SOFTWARE'):
+if 'gunicorn' in os.getenv('SERVER_SOFTWARE', ''):
     crawler.default_cache.autotrim()