diff --git a/lib/options.js b/lib/options.js
index 15612165..acc1e3a2 100644
--- a/lib/options.js
+++ b/lib/options.js
@@ -87,7 +87,7 @@ export function normalizeOptions(options) {
     const sourceType = normalizeSourceType(options.sourceType);
     const ranges = options.range === true;
     const locations = options.loc === true;
-    const allowReserved = ecmaVersion === 3 ? "never" : null;
+    const allowReserved = ecmaVersion === 3 ? "never" : false;
 
     if (sourceType === "module" && ecmaVersion < 6) {
         throw new Error("sourceType 'module' is not supported when ecmaVersion < 2015. Consider adding `{ ecmaVersion: 2015 }` to the parser options.");