diff --git a/gunicorn/reloader.py b/gunicorn/reloader.py
index 219ffa83..130e3d60 100644
--- a/gunicorn/reloader.py
+++ b/gunicorn/reloader.py
@@ -26,7 +26,7 @@ class Reloader(threading.Thread):
     def get_files(self):
         fnames = [
             re.sub('py[co]$', 'py', module.__file__)
-            for module in sys.modules.values()
+            for module in list(sys.modules.values())
             if hasattr(module, '__file__')
         ]