diff --git a/snippets/invertKeyValues.md b/snippets/invertKeyValues.md
index 2d4302145..e50ea0912 100644
--- a/snippets/invertKeyValues.md
+++ b/snippets/invertKeyValues.md
@@ -1,17 +1,21 @@
 ### invertKeyValues
 
-Inverts the key-value pairs of an object, without mutating it.
+Inverts the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.
 
-Use `Object.keys()` and `Array.reduce()` to invert the key-value pairs of an object.
+Use `Object.keys()` and `Array.reduce()` to invert the key-value pairs of an object and apply the function provided (if any).
+Omit the second argument, `fn`, to get the inverted keys without applying a function to them.
 
 ```js
-const invertKeyValues = obj =>
+const invertKeyValues = (obj, fn) =>
   Object.keys(obj).reduce((acc, key) => {
-    acc[obj[key]] = key;
+    const val = fn ? fn(obj[key]) : obj[key];
+    acc[val] = acc[val] || [];
+    acc[val].push(key);
     return acc;
   }, {});
 ```
 
 ```js
-invertKeyValues({ name: 'John', age: 20 }); // { 20: 'age', John: 'name' }
+invertKeyValues({ a: 1, b: 2, c: 1 }); // { 1: [ 'a', 'c' ], 2: [ 'b' ] }
+invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value); // { group1: [ 'a', 'c' ], group2: [ 'b' ] }
 ```
diff --git a/tag_database b/tag_database
index 6b69c3f7d..17a08401f 100644
--- a/tag_database
+++ b/tag_database
@@ -85,7 +85,7 @@ initializeArrayWithRangeRight:array,math
 initializeArrayWithValues:array,math
 inRange:math
 intersection:array,math
-invertKeyValues:object
+invertKeyValues:object,function
 is:type,array,regexp
 isAbsoluteURL:string,utility,browser,url
 isArrayLike:type,array