diff --git a/lib/utils/page.js b/lib/utils/page.js
index 727f3b35b..e2a7cd5bc 100644
--- a/lib/utils/page.js
+++ b/lib/utils/page.js
@@ -229,7 +229,12 @@ function normalizeHtml(src, options) {
                 ($(this).attr("class") || "").split(" ")
             )
             .map(function(cl) {
+                // Markdown
                 if (cl.search("lang-") === 0) return cl.slice("lang-".length);
+
+                // Asciidoc
+                if (cl.search("language-") === 0) return cl.slice("language-".length);
+
                 return null;
             })
             .compact()