diff --git a/lib/runtime/runtime.js b/lib/runtime/runtime.js
index 12cce48..bf2e8b0 100644
--- a/lib/runtime/runtime.js
+++ b/lib/runtime/runtime.js
@@ -23,7 +23,8 @@ global._init = (function() {
     } : undefined;
 
     function nowCpuTime() {
-        return isolate.cpuTime[0] * 1e3 + isolate.cpuTime[1] / 1e6;
+        const time = isolate.cpuTime;
+        return time[0] * 1e3 + time[1] / 1e6;
     }
 
     module.exports.context = context;