diff --git a/README.md b/README.md
index b8b20b8ee..32d3467e4 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# lodash v4.0.8
+# lodash v4.0.9
 
 The [lodash](https://lodash.com/) library exported as [npm packages](https://www.npmjs.com/browse/keyword/lodash-modularized) per method.
 
diff --git a/lodash.assign/README.md b/lodash.assign/README.md
index 4328741ae..47d28558f 100644
--- a/lodash.assign/README.md
+++ b/lodash.assign/README.md
@@ -1,4 +1,4 @@
-# lodash.assign v4.0.8
+# lodash.assign v4.0.9
 
 The [lodash](https://lodash.com/) method `_.assign` exported as a [Node.js](https://nodejs.org/) module.
 
@@ -15,4 +15,4 @@ In Node.js:
 var assign = require('lodash.assign');
 ```
 
-See the [documentation](https://lodash.com/docs#assign) or [package source](https://github.com/lodash/lodash/blob/4.0.8-npm-packages/lodash.assign) for more details.
+See the [documentation](https://lodash.com/docs#assign) or [package source](https://github.com/lodash/lodash/blob/4.0.9-npm-packages/lodash.assign) for more details.
diff --git a/lodash.assign/index.js b/lodash.assign/index.js
index 20eae3f55..1a5cfe552 100644
--- a/lodash.assign/index.js
+++ b/lodash.assign/index.js
@@ -1,5 +1,5 @@
 /**
- * lodash 4.0.8 (Custom Build) <https://lodash.com/>
+ * lodash (Custom Build) <https://lodash.com/>
  * Build: `lodash modularize exports="npm" -o ./`
  * Copyright jQuery Foundation and other contributors <https://jquery.org/>
  * Released under MIT license <https://lodash.com/license>
@@ -19,20 +19,6 @@ var funcTag = '[object Function]',
 /** Used to detect unsigned integer values. */
 var reIsUint = /^(?:0|[1-9]\d*)$/;
 
-/**
- * Checks if `value` is a valid array-like index.
- *
- * @private
- * @param {*} value The value to check.
- * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
- * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
- */
-function isIndex(value, length) {
-  value = (typeof value == 'number' || reIsUint.test(value)) ? +value : -1;
-  length = length == null ? MAX_SAFE_INTEGER : length;
-  return value > -1 && value % 1 == 0 && value < length;
-}
-
 /** Used for built-in method references. */
 var objectProto = Object.prototype;
 
@@ -75,7 +61,7 @@ function assignValue(object, key, value) {
  *
  * @private
  * @param {string} key The key of the property to get.
- * @returns {Function} Returns the new function.
+ * @returns {Function} Returns the new accessor function.
  */
 function baseProperty(key) {
   return function(object) {
@@ -125,7 +111,7 @@ function createAssigner(assigner) {
         customizer = length > 1 ? sources[length - 1] : undefined,
         guard = length > 2 ? sources[2] : undefined;
 
-    customizer = typeof customizer == 'function'
+    customizer = (assigner.length > 3 && typeof customizer == 'function')
       ? (length--, customizer)
       : undefined;
 
@@ -157,6 +143,21 @@ function createAssigner(assigner) {
  */
 var getLength = baseProperty('length');
 
+/**
+ * Checks if `value` is a valid array-like index.
+ *
+ * @private
+ * @param {*} value The value to check.
+ * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
+ * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
+ */
+function isIndex(value, length) {
+  length = length == null ? MAX_SAFE_INTEGER : length;
+  return !!length &&
+    (typeof value == 'number' || reIsUint.test(value)) &&
+    (value > -1 && value % 1 == 0 && value < length);
+}
+
 /**
  * Checks if the given arguments are from an iteratee call.
  *
@@ -363,6 +364,7 @@ function isObject(value) {
  * @param {Object} object The destination object.
  * @param {...Object} [sources] The source objects.
  * @returns {Object} Returns `object`.
+ * @see _.assignIn
  * @example
  *
  * function Foo() {
diff --git a/lodash.assign/package.json b/lodash.assign/package.json
index 3c02f35a7..ce404b881 100644
--- a/lodash.assign/package.json
+++ b/lodash.assign/package.json
@@ -1,6 +1,6 @@
 {
   "name": "lodash.assign",
-  "version": "4.0.8",
+  "version": "4.0.9",
   "description": "The lodash method `_.assign` exported as a module.",
   "homepage": "https://lodash.com/",
   "icon": "https://lodash.com/icon.svg",
diff --git a/lodash.assignin/README.md b/lodash.assignin/README.md
index 5b5bf7709..fcaa57ef6 100644
--- a/lodash.assignin/README.md
+++ b/lodash.assignin/README.md
@@ -1,4 +1,4 @@
-# lodash.assignin v4.0.8
+# lodash.assignin v4.0.9
 
 The [lodash](https://lodash.com/) method `_.assignIn` exported as a [Node.js](https://nodejs.org/) module.
 
@@ -15,4 +15,4 @@ In Node.js:
 var assignIn = require('lodash.assignin');
 ```
 
-See the [documentation](https://lodash.com/docs#assignIn) or [package source](https://github.com/lodash/lodash/blob/4.0.8-npm-packages/lodash.assignin) for more details.
+See the [documentation](https://lodash.com/docs#assignIn) or [package source](https://github.com/lodash/lodash/blob/4.0.9-npm-packages/lodash.assignin) for more details.
diff --git a/lodash.assignin/index.js b/lodash.assignin/index.js
index 9185f1fcf..44d360738 100644
--- a/lodash.assignin/index.js
+++ b/lodash.assignin/index.js
@@ -1,5 +1,5 @@
 /**
- * lodash 4.0.8 (Custom Build) <https://lodash.com/>
+ * lodash (Custom Build) <https://lodash.com/>
  * Build: `lodash modularize exports="npm" -o ./`
  * Copyright jQuery Foundation and other contributors <https://jquery.org/>
  * Released under MIT license <https://lodash.com/license>
@@ -19,20 +19,6 @@ var funcTag = '[object Function]',
 /** Used to detect unsigned integer values. */
 var reIsUint = /^(?:0|[1-9]\d*)$/;
 
-/**
- * Checks if `value` is a valid array-like index.
- *
- * @private
- * @param {*} value The value to check.
- * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
- * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
- */
-function isIndex(value, length) {
-  value = (typeof value == 'number' || reIsUint.test(value)) ? +value : -1;
-  length = length == null ? MAX_SAFE_INTEGER : length;
-  return value > -1 && value % 1 == 0 && value < length;
-}
-
 /** Used for built-in method references. */
 var objectProto = Object.prototype;
 
@@ -75,7 +61,7 @@ function assignValue(object, key, value) {
  *
  * @private
  * @param {string} key The key of the property to get.
- * @returns {Function} Returns the new function.
+ * @returns {Function} Returns the new accessor function.
  */
 function baseProperty(key) {
   return function(object) {
@@ -125,7 +111,7 @@ function createAssigner(assigner) {
         customizer = length > 1 ? sources[length - 1] : undefined,
         guard = length > 2 ? sources[2] : undefined;
 
-    customizer = typeof customizer == 'function'
+    customizer = (assigner.length > 3 && typeof customizer == 'function')
       ? (length--, customizer)
       : undefined;
 
@@ -157,6 +143,21 @@ function createAssigner(assigner) {
  */
 var getLength = baseProperty('length');
 
+/**
+ * Checks if `value` is a valid array-like index.
+ *
+ * @private
+ * @param {*} value The value to check.
+ * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
+ * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
+ */
+function isIndex(value, length) {
+  length = length == null ? MAX_SAFE_INTEGER : length;
+  return !!length &&
+    (typeof value == 'number' || reIsUint.test(value)) &&
+    (value > -1 && value % 1 == 0 && value < length);
+}
+
 /**
  * Checks if the given arguments are from an iteratee call.
  *
@@ -362,6 +363,7 @@ function isObject(value) {
  * @param {Object} object The destination object.
  * @param {...Object} [sources] The source objects.
  * @returns {Object} Returns `object`.
+ * @see _.assign
  * @example
  *
  * function Foo() {
diff --git a/lodash.assignin/package.json b/lodash.assignin/package.json
index 2323a27cb..9debe8d4e 100644
--- a/lodash.assignin/package.json
+++ b/lodash.assignin/package.json
@@ -1,6 +1,6 @@
 {
   "name": "lodash.assignin",
-  "version": "4.0.8",
+  "version": "4.0.9",
   "description": "The lodash method `_.assignIn` exported as a module.",
   "homepage": "https://lodash.com/",
   "icon": "https://lodash.com/icon.svg",