diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index 9420dfda58..b22bf8220e 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -46,9 +46,39 @@ File.helpers = [
   "get"
 ];
 
+File.validOptions = [
+  "filename",
+  "fileNameRelative",
+  "blacklist",
+  "whitelist",
+  "optional",
+  "modules",
+  "sourceMap",
+  "sourceMapName",
+  "sourceFileName",
+  "sourceRoot",
+  "moduleRoot",
+  "moduleIds",
+  "runtime",
+  "comments",
+  "reactCompat",
+  "keepModuleIdExtensions",
+  "code",
+  "ast",
+  "format",
+  "playground",
+  "experimental"
+];
+
 File.normaliseOptions = function (opts) {
   opts = _.cloneDeep(opts || {});
 
+  for (var key in opts) {
+    if (File.validOptions.indexOf(key) < 0) {
+      throw new ReferenceError("Unknown option: " + key);
+    }
+  }
+
   _.defaults(opts, {
     keepModuleIdExtensions: false,
     experimental:           false,