diff --git a/lib/register.js b/lib/register.js
index 705ee15d..22a89712 100644
--- a/lib/register.js
+++ b/lib/register.js
@@ -369,16 +369,19 @@
       entry.esModule = {};
 
       // don't trigger getters/setters in environments that support them
-      if (Object.getOwnPropertyDescriptor) {
-        var d;
-        for (var p in exports)
-          if (d = Object.getOwnPropertyDescriptor(exports, p))
-            Object.defineProperty(entry.esModule, p, d);
-      } else {
-        var hasOwnProperty = exports && exports.hasOwnProperty;
-        for (var p in exports) {
-          if (!hasOwnProperty || exports.hasOwnProperty(p))
-            entry.esModule[p] = exports[p];
+      if (typeof exports == 'object' || typeof exports == 'function') {
+        if (Object.getOwnPropertyDescriptor) {
+          var d;
+          for (var p in exports)
+            if (d = Object.getOwnPropertyDescriptor(exports, p))
+              Object.defineProperty(entry.esModule, p, d);
+        }
+        else {
+          var hasOwnProperty = exports && exports.hasOwnProperty;
+          for (var p in exports) {
+            if (!hasOwnProperty || exports.hasOwnProperty(p))
+              entry.esModule[p] = exports[p];
+          }
         }
       }
       entry.esModule['default'] = exports;