diff --git a/src/librustdoc/html/static/.eslintrc.js b/src/librustdoc/html/static/.eslintrc.js
index 627c3e0780b..ab0bff95228 100644
--- a/src/librustdoc/html/static/.eslintrc.js
+++ b/src/librustdoc/html/static/.eslintrc.js
@@ -76,5 +76,6 @@ module.exports = {
         "no-self-compare": "error",
         "no-template-curly-in-string": "error",
         "block-scoped-var": "error",
+        "guard-for-in": "error",
     }
 };