diff --git a/lodash.js b/lodash.js
index 1f8aafcfc..04d9ffd80 100644
--- a/lodash.js
+++ b/lodash.js
@@ -13173,6 +13173,11 @@
      * // => { '1': 'c', '2': 'b' }
      */
     var invert = createInverter(function(result, value, key) {
+      if (value != null &&
+          typeof value.toString != 'function') {
+        value = nativeObjectToString.call(value);
+      }
+
       result[value] = key;
     }, constant(identity));
 
@@ -13203,6 +13208,11 @@
      * // => { 'group1': ['a', 'c'], 'group2': ['b'] }
      */
     var invertBy = createInverter(function(result, value, key) {
+      if (value != null &&
+          typeof value.toString != 'function') {
+        value = nativeObjectToString.call(value);
+      }
+
       if (hasOwnProperty.call(result, value)) {
         result[value].push(key);
       } else {