diff --git a/judge/jinja2/markdown/__init__.py b/judge/jinja2/markdown/__init__.py
index b0bc6f6..fa78791 100644
--- a/judge/jinja2/markdown/__init__.py
+++ b/judge/jinja2/markdown/__init__.py
@@ -36,7 +36,7 @@ EXTENSION_CONFIGS = {
     },
 }
 
-ALLOWED_TAGS = bleach.sanitizer.ALLOWED_TAGS + [
+ALLOWED_TAGS = list(bleach.sanitizer.ALLOWED_TAGS) + [
     "img",
     "center",
     "iframe",