diff --git a/README.md b/README.md
index 1d35a1b..59a1188 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@ This module extends the `TextField`, `TextareaField` and `HTMLEditorField` class
 
 ## Requirements
 
-SilverStripe 3.1+ (3.3 tested)
+SilverStripe 4.0+ (3.1+ in previous releases)
 
 ## Installation
 
@@ -16,10 +16,6 @@ SilverStripe 3.1+ (3.3 tested)
 
 [Packagist listing](https://packagist.org/packages/jonom/silverstripe-text-target-length) and [installation instructions](http://doc.silverstripe.org/framework/en/trunk/installation/composer#adding-modules-to-your-project)
 
-### Manually
-
-I promise it's worth your time to learn how to use Composer. If painless updating isn't your thing though you can download and extract this project, rename the module folder 'text-target-length', place it in your project root and run a dev/build?flush=1.
-
 ## How to use
 
 With the module installed you can call call `setTargetLength()` on `TextField`, `TextareaField` and `HTMLEditorField` form fields.
diff --git a/_config.php b/_config.php
index 8093b43..a4abe2d 100644
--- a/_config.php
+++ b/_config.php
@@ -1,6 +1,2 @@
 <?php
 
-if (!defined('TEXTTARGETLENGTH_DIR')) {
-    //Assumes this module is installed in web root
-    define('TEXTTARGETLENGTH_DIR', basename(dirname(__FILE__)));
-}
diff --git a/_config/config.yml b/_config/config.yml
index a2c2cbe..2c0766d 100644
--- a/_config/config.yml
+++ b/_config/config.yml
@@ -1,12 +1,12 @@
 ---
 Name: text-target-length
 ---
-TextField:
+SilverStripe\Forms\TextareaField:
   extensions:
-    - TextTargetLengthExtension
-TextareaField:
+    - JonoM\SilverStripeTextTargetLength\TextTargetLengthExtension
+SilverStripe\Forms\TextareaField:
   extensions:
-    - TextTargetLengthExtension
-HTMLEditorField:
+    - JonoM\SilverStripeTextTargetLength\TextTargetLengthExtension
+SilverStripe\Forms\HTMLEditor\HTMLEditorField:
   extensions:
-    - TextTargetLengthExtension
+    - JonoM\SilverStripeTextTargetLength\TextTargetLengthExtension
diff --git a/css/text-target-length.css b/client/css/text-target-length.css
similarity index 100%
rename from css/text-target-length.css
rename to client/css/text-target-length.css
diff --git a/javascript/text-target-length.js b/client/javascript/text-target-length.js
old mode 100755
new mode 100644
similarity index 100%
rename from javascript/text-target-length.js
rename to client/javascript/text-target-length.js
diff --git a/code/TextTargetLengthExtension.php b/code/TextTargetLengthExtension.php
deleted file mode 100755
index e0ce788..0000000
--- a/code/TextTargetLengthExtension.php
+++ /dev/null
@@ -1,51 +0,0 @@
-<?php
-
-/**
- * Apply this extension to text editing form field such as TextareaField
- * to allow setting of ideal, min and max lengths. These are
- * soft limits only, to give CMS users an idea of target length.
- */
-class TextTargetLengthExtension extends Extension
-{
-
-	/**
-	 * Set a target character length for text in a field.
-	 *
-	 * @param Int $idealCharCount the ideal number of characters for this text
-	 * @param Int $minCharCount (default: null) the minimum number of characters for this text
-	 * @param Int $maxCharCount (default: null) the maximum number of characters for this text
-	 * @return FormField
-	 */
-	public function setTargetLength($idealCharCount, $minCharCount = null, $maxCharCount = null)
-	{
-        $field = $this->owner;
-        $idealCharCount = (int)$idealCharCount;
-    	if (!$idealCharCount > 0) return $field;
-
-    	// Set defaults
-		if ($minCharCount === null) $minCharCount = round($idealCharCount * .75);
-		if ($maxCharCount === null) $maxCharCount = round($idealCharCount * 1.25);
-
-		// Validate
-		if (!($maxCharCount >= $idealCharCount && $idealCharCount >= $minCharCount)) return $field;
-
-		// Activate
-		$field->addExtraClass('target-length');
-		$field->setAttribute('data-target-ideal-length', $idealCharCount);
-		$field->setAttribute('data-target-min-length', $minCharCount);
-		$field->setAttribute('data-target-max-length', $maxCharCount);
-
-        $field->setAttribute('data-hint-length-target', _t('TextTargetLength.LengthTarget', 'Length target: <b>{value}%</b> <i>{remark}</i>'));
-        $field->setAttribute('data-hint-length-tooshort', _t('TextTargetLength.LengthTooShort', 'Keep going!'));
-        $field->setAttribute('data-hint-length-toolong', _t('TextTargetLength.LengthTooLong', 'Too long'));
-        $field->setAttribute('data-hint-length-adequate', _t('TextTargetLength.LengthAdequate', 'Okay'));
-        $field->setAttribute('data-hint-length-ideal', _t('TextTargetLength.LengthIdeal', 'Great!'));
-
-        Requirements::javascript(FRAMEWORK_DIR.'/thirdparty/jquery/jquery.js');
-        Requirements::javascript(FRAMEWORK_DIR.'/thirdparty/jquery-entwine/dist/jquery.entwine-dist.js');
-        Requirements::javascript(TEXTTARGETLENGTH_DIR.'/javascript/text-target-length.js');
-        Requirements::css(TEXTTARGETLENGTH_DIR.'/css/text-target-length.css');
-
-		return $field;
-	}
-}
diff --git a/composer.json b/composer.json
index 5afc7f8..9f362c7 100644
--- a/composer.json
+++ b/composer.json
@@ -1,17 +1,24 @@
 {
-	"name": "jonom/silverstripe-text-target-length",
-	"description": "Set character length recommendations on SilverStripe text form fields",
-	"type": "silverstripe-module",
-	"keywords": ["silverstripe", "textfield", "textareafield", "target"],
-	"license": "BSD-3-Clause",
-	"authors": [{
-		"name": "Jonathon Menz",
-		"homepage": "http://jonathonmenz.com"
-	}],
-	"require": {
-		"silverstripe/framework": "^3.1"
-	},
-	"extra": {
-		"installer-name": "text-target-length"
-	}
+    "name": "jonom/silverstripe-text-target-length",
+    "description": "Set character length recommendations on SilverStripe text form fields",
+    "type": "silverstripe-vendormodule",
+    "keywords": ["silverstripe", "textfield", "textareafield", "target"],
+    "license": "BSD-3-Clause",
+    "authors": [{
+        "name": "Jonathon Menz",
+        "homepage": "http://jonathonmenz.com"
+    }],
+    "require": {
+        "silverstripe/framework": "^4.0"
+    },
+    "autoload": {
+        "psr-4": {
+            "JonoM\\SilverStripeTextTargetLength\\": "src/"
+        }
+    },
+    "extra": {
+        "expose": [
+            "client"
+        ]
+    }
 }
diff --git a/src/TextTargetLengthExtension.php b/src/TextTargetLengthExtension.php
new file mode 100644
index 0000000..24ab778
--- /dev/null
+++ b/src/TextTargetLengthExtension.php
@@ -0,0 +1,55 @@
+<?php
+
+namespace JonoM\SilverStripeTextTargetLength;
+
+use SilverStripe\Core\Extension;
+use SilverStripe\View\Requirements;
+
+/**
+ * Apply this extension to text editing form field such as TextareaField
+ * to allow setting of ideal, min and max lengths. These are
+ * soft limits only, to give CMS users an idea of target length.
+ */
+class TextTargetLengthExtension extends Extension
+{
+    /**
+     * Set a target character length for text in a field.
+     *
+     * @param Int $idealCharCount the ideal number of characters for this text
+     * @param Int $minCharCount (default: null) the minimum number of characters for this text
+     * @param Int $maxCharCount (default: null) the maximum number of characters for this text
+     * @return FormField
+     */
+    public function setTargetLength($idealCharCount, $minCharCount = null, $maxCharCount = null)
+    {
+        $field = $this->owner;
+        $idealCharCount = (int)$idealCharCount;
+        if (!$idealCharCount > 0) return $field;
+
+        // Set defaults
+        if ($minCharCount === null) $minCharCount = round($idealCharCount * .75);
+        if ($maxCharCount === null) $maxCharCount = round($idealCharCount * 1.25);
+
+        // Validate
+        if (!($maxCharCount >= $idealCharCount && $idealCharCount >= $minCharCount)) return $field;
+
+        // Activate
+        $field->addExtraClass('target-length');
+        $field->setAttribute('data-target-ideal-length', $idealCharCount);
+        $field->setAttribute('data-target-min-length', $minCharCount);
+        $field->setAttribute('data-target-max-length', $maxCharCount);
+
+        $field->setAttribute('data-hint-length-target', _t('TextTargetLength.LengthTarget', 'Length target: <b>{value}%</b> <i>{remark}</i>'));
+        $field->setAttribute('data-hint-length-tooshort', _t('TextTargetLength.LengthTooShort', 'Keep going!'));
+        $field->setAttribute('data-hint-length-toolong', _t('TextTargetLength.LengthTooLong', 'Too long'));
+        $field->setAttribute('data-hint-length-adequate', _t('TextTargetLength.LengthAdequate', 'Okay'));
+        $field->setAttribute('data-hint-length-ideal', _t('TextTargetLength.LengthIdeal', 'Great!'));
+
+        Requirements::javascript('silverstripe/admin:thirdparty/jquery/jquery.js');
+        Requirements::javascript('silverstripe/admin:thirdparty/jquery-entwine/dist/jquery.entwine-dist.js');
+        Requirements::javascript('jonom/silverstripe-text-target-length:client/javascript/text-target-length.js');
+        Requirements::css('jonom/silverstripe-text-target-length:client/css/text-target-length.css');
+
+        return $field;
+    }
+}