--- a/devtools/client/shared/vendor/stringvalidator/tests/unit/test_validators.js
+++ b/devtools/client/shared/vendor/stringvalidator/tests/unit/test_validators.js
@@ -1806,17 +1806,17 @@ function run_test() {
       });
       test({
         validator: 'isBefore',
         valid: [
           '2000-08-04',
           new Date(0).toString(),
           new Date(Date.now() - 86400000).toString(),
         ],
-        invalid: ['2100-07-02', new Date(2017, 10, 10).toString()],
+        invalid: ['2100-07-02', new Date(2097, 10, 10).toString()],
       });
       test({
         validator: 'isBefore',
         args: ['2011-08-03'],
         valid: ['1999-12-31'],
         invalid: ['invalid date'],
       });
       test({