diff --git a/index.js b/index.js
index aa2bb39..bdcfdc8 100644
--- a/index.js
+++ b/index.js
@@ -66,7 +66,7 @@ module.exports = function kindOf(val) {
 };
 
 function ctorName(val) {
-  return val.constructor ? val.constructor.name : null;
+  return val.constructor && typeof val.constructor === 'function' ? val.constructor.name : null;
 }
 
 function isArray(val) {