diff --git a/src/style-spec/error/validation_error.js b/src/style-spec/error/validation_error.js
index 5a55e34652e..dce87fab40d 100644
--- a/src/style-spec/error/validation_error.js
+++ b/src/style-spec/error/validation_error.js
@@ -2,11 +2,8 @@
 
 const format = require('util').format;
 
-function ValidationError(key, value /*, message, ...*/) {
-    this.message = (
-        (key ? `${key}: ` : '') +
-        format.apply(format, Array.prototype.slice.call(arguments, 2))
-    );
+function ValidationError(key, value, ...args) {
+    this.message = (key ? `${key}: ` : '') + format.apply(format, args);
 
     if (value !== null && value !== undefined && value.__line__) {
         this.line = value.__line__;
diff --git a/src/style-spec/function/index.js b/src/style-spec/function/index.js
index 1a72e9de524..7a22b919cbe 100644
--- a/src/style-spec/function/index.js
+++ b/src/style-spec/function/index.js
@@ -196,9 +196,9 @@ function evaluateExponentialFunction(parameters, propertySpec, input) {
     const interp = interpolate[propertySpec.type] || identityFunction;
 
     if (typeof outputLower === 'function') {
-        return function() {
-            const evaluatedLower = outputLower.apply(undefined, arguments);
-            const evaluatedUpper = outputUpper.apply(undefined, arguments);
+        return function(...args) {
+            const evaluatedLower = outputLower.apply(undefined, args);
+            const evaluatedUpper = outputUpper.apply(undefined, args);
             // Special case for fill-outline-color, which has no spec default.
             if (evaluatedLower === undefined || evaluatedUpper === undefined) {
                 return undefined;
diff --git a/src/style-spec/util/extend.js b/src/style-spec/util/extend.js
index a3a746cad40..3e1efd69ccb 100644
--- a/src/style-spec/util/extend.js
+++ b/src/style-spec/util/extend.js
@@ -1,8 +1,7 @@
 'use strict';
 
-module.exports = function (output) {
-    for (let i = 1; i < arguments.length; i++) {
-        const input = arguments[i];
+module.exports = function (output, ...inputs) {
+    for (const input of inputs) {
         for (const k in input) {
             output[k] = input[k];
         }
diff --git a/src/util/util.js b/src/util/util.js
index 54bf987487c..a52c1361289 100644
--- a/src/util/util.js
+++ b/src/util/util.js
@@ -139,13 +139,11 @@ exports.keysDifference = function (obj: {[key: string]: mixed}, other: {[key: st
  * source objects.
  *
  * @param dest destination object
- * @param {...Object} sources sources from which properties are pulled
+ * @param sources sources from which properties are pulled
  * @private
  */
-// eslint-disable-next-line no-unused-vars
-exports.extend = function (dest: Object, source0: Object, source1?: Object, source2?: Object): Object {
-    for (let i = 1; i < arguments.length; i++) {
-        const src = arguments[i];
+exports.extend = function (dest: Object, ...sources: Array<Object>): Object {
+    for (const src of sources) {
         for (const k in src) {
             dest[k] = src[k];
         }