--- a/testing/marionette/driver.js
+++ b/testing/marionette/driver.js
@@ -854,17 +854,17 @@ GeckoDriver.prototype.executeScript = fu
  *     JavaScript notion of null or undefined.
  *
  * @throws ScriptTimeoutError
  *     If the script was interrupted due to reaching the {@code
  *     scriptTimeout} or default timeout.
  * @throws JavaScriptError
  *     If an Error was thrown whilst evaluating the script.
  */
-GeckoDriver.prototype.executeAsyncScript = function(cmd, resp) {
+GeckoDriver.prototype.executeAsyncScript = function*(cmd, resp) {
   let {script, args, scriptTimeout} = cmd.parameters;
   scriptTimeout = scriptTimeout || this.scriptTimeout;
 
   let opts = {
     sandboxName: cmd.parameters.sandbox,
     newSandbox: !!(typeof cmd.parameters.newSandbox == "undefined") ||
         cmd.parameters.newSandbox,
     filename: cmd.parameters.filename,
@@ -904,17 +904,17 @@ GeckoDriver.prototype.execute_ = functio
 };
 
 /**
  * Execute pure JavaScript.  Used to execute simpletest harness tests,
  * which are like mochitests only injected using Marionette.
  *
  * Scripts are expected to call the {@code finish} global when done.
  */
-GeckoDriver.prototype.executeJSScript = function(cmd, resp) {
+GeckoDriver.prototype.executeJSScript = function*(cmd, resp) {
   let {script, args, scriptTimeout} = cmd.parameters;
   scriptTimeout = scriptTimeout || this.scriptTimeout;
 
   let opts = {
     filename: cmd.parameters.filename,
     line: cmd.parameters.line,
     async: cmd.parameters.async,
   };