diff --git a/test/parallel/test-v8-flags.js b/test/parallel/test-v8-flags.js
index cee924d5b13068..50cff9ecefceac 100644
--- a/test/parallel/test-v8-flags.js
+++ b/test/parallel/test-v8-flags.js
@@ -4,10 +4,13 @@ var assert = require('assert');
 var v8 = require('v8');
 var vm = require('vm');
 
+// Note: changing V8 flags after an isolate started is not guaranteed to work.
+// Specifically here, V8 may cache compiled scripts between the flip of the
+// flag. We use a different script each time to work around this problem.
 v8.setFlagsFromString('--allow_natives_syntax');
 assert(eval('%_IsSmi(42)'));
-assert(vm.runInThisContext('%_IsSmi(42)'));
+assert(vm.runInThisContext('%_IsSmi(43)'));
 
 v8.setFlagsFromString('--noallow_natives_syntax');
-assert.throws(function() { eval('%_IsSmi(42)'); }, SyntaxError);
-assert.throws(function() { vm.runInThisContext('%_IsSmi(42)'); }, SyntaxError);
+assert.throws(function() { eval('%_IsSmi(44)'); }, SyntaxError);
+assert.throws(function() { vm.runInThisContext('%_IsSmi(45)'); }, SyntaxError);