diff --git a/docs/x509/reference.rst b/docs/x509/reference.rst
index 01a5d94..8bb3f40 100644
--- a/docs/x509/reference.rst
+++ b/docs/x509/reference.rst
@@ -2436,7 +2436,7 @@
 .. class:: UnsupportedExtension
 
     This is raised when a certificate contains an unsupported extension type
-    that is marked critical.
+    that is marked ``critical``.
 
     .. attribute:: oid