diff --git a/feedparser/html.py b/feedparser/html.py
index bbb90389..826e4a11 100644
--- a/feedparser/html.py
+++ b/feedparser/html.py
@@ -152,7 +152,7 @@ def feed(self, data):
         :rtype: None
         """
 
-        data = re.sub(r"<!((?!DOCTYPE|--|\[))", r"&lt;!\1", data, re.IGNORECASE)
+        data = re.sub(r"<!((?!DOCTYPE|--|\[))", r"&lt;!\1", data, flags=re.IGNORECASE)
         data = re.sub(r"<([^<>\s]+?)\s*/>", self._shorttag_replace, data)
         data = data.replace("&#39;", "'")
         data = data.replace("&#34;", '"')