diff --git a/invert.js b/invert.js
index 3cb243054..1078a2534 100644
--- a/invert.js
+++ b/invert.js
@@ -1,3 +1,5 @@
+const toString = Object.prototype.toString
+
 /**
  * Creates an object composed of the inverted keys and values of `object`.
  * If `object` contains duplicate values, subsequent values overwrite
@@ -17,6 +19,9 @@
 function invert(object) {
   const result = {}
   Object.keys(object).forEach((value, key) => {
+    if (value != null && typeof value.toString != 'function') {
+      value = toString.call(value)
+    }
     result[value] = key
   })
   return result