diff --git a/lib/renderer-markdown.js b/lib/renderer-markdown.js
index 2eeaf59..16d7321 100644
--- a/lib/renderer-markdown.js
+++ b/lib/renderer-markdown.js
@@ -16,7 +16,7 @@ const readFile = util.promisify(fs.readFile);
 Handlebars.registerHelper("isExternalRef", function (value) {
   return (
     typeof value === "string" &&
-    (value.match(/^(.+)#/) || value.match(/^(.+)\.(json|yml)$/))
+    (value.match(/^(.+)#/) || value.match(/^(.+)\.(json|yaml|yml)$/))
   );
 });
 Handlebars.registerHelper("getHtmlAnchorForRef", function (ref, label) {