diff --git a/src/esmock.js b/src/esmock.js
index d5a28164..dde113b9 100644
--- a/src/esmock.js
+++ b/src/esmock.js
@@ -9,7 +9,7 @@ import esmockErr from './esmockErr.js'
 
 const esmockGo = opts => async (...args) => {
   const [moduleId, parent, defs, gdefs, opt] = esmockArgs(args, opts)
-  if (!esmockRegister && !await esmockLoader())
+  if (!esmockRegister.register() && !await esmockLoader())
     throw esmockErr.errMissingLoader()
 
   const fileURLKey = await esmockModule(moduleId, parent, defs, gdefs, opt)
diff --git a/src/esmockRegister.js b/src/esmockRegister.js
index 75f376e2..748cc001 100644
--- a/src/esmockRegister.js
+++ b/src/esmockRegister.js
@@ -19,10 +19,10 @@ const register = (res => () => {
   return res
 })()
 
-export default msg => {
+export default Object.assign(msg => {
   if (register()) {
     channel.port1.postMessage(msg)
   } else if (typeof global.postMessageEsmk === 'function') {
     global.postMessageEsmk(msg)
   }
-}
+}, { register })