1 files changed, 3 insertions, 0 deletions
diff --git a/.eslintrc.js b/.eslintrc.js
index a7a8862926..3d3ad2b80a 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -7,6 +7,9 @@ module.exports = {
   ],
   "rules": {
     "mozilla/import-globals": "warn",
+
+    // No (!foo in bar) or (!object instanceof Class)
+    "no-unsafe-negation": "error",
   },
   "env": {
     "es6": true