diff --git a/course/page/code.py b/course/page/code.py
index c7ed5a2109a9e3c2560e831a476a8dd63f36d284..76963871c77be41496ed52f3e66f63bb77a38652 100644
--- a/course/page/code.py
+++ b/course/page/code.py
@@ -906,6 +906,9 @@ class PythonCodeQuestion(PageBaseWithTitle, PageBaseWithValue):
                     else:
                         return False
 
+                if not isinstance(s, six.text_type):
+                    return _("(Non-string in 'HTML' output filtered out)")
+
                 return bleach.clean(s,
                         tags=bleach.ALLOWED_TAGS + ["audio", "video", "source"],
                         attributes={