diff --git a/.eslintrc.js b/.eslintrc.js
index b52c703df..c882910a6 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -11,12 +11,13 @@ module.exports = {
     },
     extends: ["eslint:recommended", "google"],
     rules: {
-        // rules we've always adhered to
+        // rules we've always adhered to or now do
         "max-len": ["error", {
             code: 90,
             ignoreComments: true,
         }],
         curly: ["error", "multi-line"],
+        "prefer-const": ["error"],
 
         // loosen jsdoc requirements a little
         "require-jsdoc": ["error", {
@@ -55,7 +56,6 @@ module.exports = {
         "padded-blocks": ["warn"],
         "no-extend-native": ["warn"],
         "camelcase": ["warn"],
-        "prefer-const": ["warn"],
 
     }
 }
diff --git a/package.json b/package.json
index 26cf0ad08..e82d4c73b 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,7 @@
     "build": "babel -s -d lib src && rimraf dist && mkdir dist && browserify --exclude olm browser-index.js -o dist/browser-matrix.js --ignore-missing && uglifyjs -c -m -o dist/browser-matrix.min.js dist/browser-matrix.js",
     "dist": "npm run build",
     "watch": "watchify --exclude olm browser-index.js -o dist/browser-matrix-dev.js -v",
-    "lint": "eslint --max-warnings 122 src spec",
+    "lint": "eslint --max-warnings 121 src spec",
     "prepublish": "npm run build && git rev-parse HEAD > git-revision.txt"
   },
   "repository": {
diff --git a/src/utils.js b/src/utils.js
index 662dee619..66d243ece 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -414,7 +414,7 @@ module.exports.runPolyfills = function() {
     // Reference: http://es5.github.io/#x15.4.4.19
     if (!Array.prototype.map) {
       Array.prototype.map = function(callback, thisArg) {
-        let T, A, k;
+        let T, k;
 
         if (this === null || this === undefined) {
           throw new TypeError(' this is null or not defined');
@@ -443,7 +443,7 @@ module.exports.runPolyfills = function() {
         // 6. Let A be a new array created as if by the expression new Array(len)
         //    where Array is the standard built-in constructor with that name and
         //    len is the value of len.
-        A = new Array(len);
+        const A = new Array(len);
 
         // 7. Let k be 0
         k = 0;