diff --git a/build-system/tasks/validator.js b/build-system/tasks/validator.js
index e6c3c1233a7b..bbe95009f3a6 100644
--- a/build-system/tasks/validator.js
+++ b/build-system/tasks/validator.js
@@ -15,22 +15,27 @@
  */
 'use strict';
 
+const argv = require('minimist')(process.argv.slice(2));
 const gulp = require('gulp-help')(require('gulp'));
 const {execOrDie} = require('../exec');
 
+let validatorArgs = '';
+if (argv.update_tests) {
+  validatorArgs += ' --update_tests';
+}
 
 /**
  * Simple wrapper around the python based validator build.
  */
 function validator() {
-  execOrDie('cd validator && python build.py');
+  execOrDie('cd validator && python build.py' + validatorArgs);
 }
 
 /**
  * Simple wrapper around the python based validator webui build.
  */
 function validatorWebui() {
-  execOrDie('cd validator/webui && python build.py');
+  execOrDie('cd validator/webui && python build.py' + validatorArgs);
 }
 
 gulp.task('validator', 'Builds and tests the AMP validator.', validator);