diff --git a/src/types.js b/src/types.js
index ddbf13d..5f885d0 100644
--- a/src/types.js
+++ b/src/types.js
@@ -26,9 +26,15 @@ module.exports = function enforce(type, value) {
     }
 
     default: {
-      if (value instanceof type) return
+      if (getName(value.constructor) === getName(type)) return
     }
   }
 
-  throw new TypeError('Expected ' + (type.name || type) + ', got ' + value)
+  throw new TypeError('Expected ' + (getName(type) || type) + ', got ' + value)
+}
+
+function getName(fn) {
+  // Why not fn.name: https://kangax.github.io/compat-table/es6/#function_name_property
+  var match = fn.toString().match(/function (.*?)\(/)
+  return match ? match[1] : null
 }
diff --git a/test/types.js b/test/types.js
index 4b6c123..fe1d149 100644
--- a/test/types.js
+++ b/test/types.js
@@ -1,7 +1,7 @@
 var assert = require('assert')
 var enforceType = require('../src/types')
 
-function CustomType() {}
+function CustomType() { return "ensure non-greedy match".toUpperCase() }
 
 var types = ['Array', 'Boolean', 'Buffer', 'Number', 'String', CustomType]
 var values = [[], true, new Buffer(1), 1234, 'foobar', new CustomType()]