diff --git a/js/ctypes/tests/unit/test_jsctypes.js.in b/js/ctypes/tests/unit/test_jsctypes.js.in
index 3e0acbef2cf9..a7615c5e080c 100644
--- a/js/ctypes/tests/unit/test_jsctypes.js.in
+++ b/js/ctypes/tests/unit/test_jsctypes.js.in
@@ -223,7 +223,7 @@ function run_int64_tests(library) {
   // here, since it's binary-compatible.)
   var test_ui64_ui64 = library.declare("test_i64_i64", Types.DEFAULT, Types.UINT64, Types.UINT64);
 #ifndef XP_WIN
-  do_check_eq(test_ui64_ui64(0xfffffffffffff00), 0xfffffffffffff000);
+  do_check_eq(test_ui64_ui64(0xffffffffffff000), 0xfffffffffffff000);
 #endif
   do_check_throws(function () { test_ui64_ui64(0x10000000000000000); }, TypeError);
   do_check_throws(function () { test_ui64_ui64(-1); }, TypeError);