diff --git a/config/eslint.json b/config/eslint.json
index 2800db370..b87a6eb4e 100644
--- a/config/eslint.json
+++ b/config/eslint.json
@@ -14,7 +14,7 @@
         "Promise": true
     },
     "parserOptions": {
-        "ecmaVersion": 5
+        "ecmaVersion": 6
     },
     "extends": "eslint:recommended",
     "rules": {
diff --git a/src/util/minimal.js b/src/util/minimal.js
index 3c406dee7..35008ecc4 100644
--- a/src/util/minimal.js
+++ b/src/util/minimal.js
@@ -280,13 +280,30 @@ function newError(name) {
             merge(this, properties);
     }
 
-    (CustomError.prototype = Object.create(Error.prototype)).constructor = CustomError;
-
-    Object.defineProperty(CustomError.prototype, "name", { get: function() { return name; } });
-
-    CustomError.prototype.toString = function toString() {
-        return this.name + ": " + this.message;
-    };
+    CustomError.prototype = Object.create(Error.prototype, {
+        constructor: {
+            value: CustomError,
+            writable: true,
+            enumerable: false,
+            configurable: true,
+        },
+        name: {
+            get() { return name; },
+            set: undefined,
+            enumerable: false,
+            // configurable: false would accurately preserve the behavior of
+            // the original, but I'm guessing that was not intentional.
+            // For an actual error subclass, this property would
+            // be configurable.
+            configurable: true,
+        },
+        toString: {
+            value() { return this.name + ": " + this.message; },
+            writable: true,
+            enumerable: false,
+            configurable: true,
+        },
+    });
 
     return CustomError;
 }