diff --git a/groupBy.js b/groupBy.js
index 51c109df98..03b5ea557f 100644
--- a/groupBy.js
+++ b/groupBy.js
@@ -23,6 +23,7 @@ const hasOwnProperty = Object.prototype.hasOwnProperty
  */
 function groupBy(collection, iteratee) {
   return reduce(collection, (result, value, key) => {
+    key = iteratee(value)
     if (hasOwnProperty.call(result, key)) {
       result[key].push(value)
     } else {
diff --git a/keyBy.js b/keyBy.js
index d5afc8edad..2297565bb7 100644
--- a/keyBy.js
+++ b/keyBy.js
@@ -25,7 +25,7 @@ import reduce from './reduce.js'
  */
 function keyBy(collection, iteratee) {
   return reduce(collection, (result, value, key) => (
-    baseAssignValue(result, key, value), result
+    baseAssignValue(result, iteratee(value), value), result
   ), {})
 }