diff --git a/src/TagField/Readonly.php b/src/ReadonlyTagField.php
similarity index 87%
rename from src/TagField/Readonly.php
rename to src/ReadonlyTagField.php
index 183f0b0..505a2ad 100644
--- a/src/TagField/Readonly.php
+++ b/src/ReadonlyTagField.php
@@ -1,9 +1,8 @@
 <?php
 
-namespace SilverStripe\TagField\TagField;
+namespace SilverStripe\TagField;
 
 use SilverStripe\Forms\ReadonlyField;
-use SilverStripe\TagField\TagField;
 
 /**
  * A readonly extension of TagField useful for non-editable items within the CMS.
@@ -11,7 +10,7 @@ use SilverStripe\TagField\TagField;
  * @package forms
  * @subpackage fields
  */
-class Readonly extends TagField
+class ReadonlyTagField extends TagField
 {
     /**
      * {@inheritDoc}
diff --git a/src/TagField.php b/src/TagField.php
index 218282a..9bd5fce 100644
--- a/src/TagField.php
+++ b/src/TagField.php
@@ -7,7 +7,6 @@ use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Control\HTTPResponse;
 use SilverStripe\Core\Injector\Injector;
 use SilverStripe\Forms\DropdownField;
-use SilverStripe\Forms\ReadonlyField;
 use SilverStripe\ORM\ArrayList;
 use SilverStripe\ORM\DataList;
 use SilverStripe\ORM\DataObject;
@@ -67,7 +66,7 @@ class TagField extends DropdownField
      * @param null|DataList $source
      * @param null|DataList $value
      */
-    public function __construct($name, $title = '', $source = null, $value = null)
+    public function __construct($name, $title = '', $source = array(), $value = null)
     {
         $this->setSourceList($source);
         parent::__construct($name, $title, $source, $value);
@@ -447,7 +446,7 @@ class TagField extends DropdownField
      */
     public function performReadonlyTransformation()
     {
-        $copy = $this->castedCopy(TagFieldReadonly::class);
+        $copy = $this->castedCopy(ReadonlyTagField::class);
         $copy->setSourceList($this->getSourceList());
         return $copy;
     }
diff --git a/tests/TagFieldTest.php b/tests/TagFieldTest.php
index 50c27d8..132dbe2 100755
--- a/tests/TagFieldTest.php
+++ b/tests/TagFieldTest.php
@@ -4,11 +4,11 @@ namespace SilverStripe\TagField\Tests;
 
 use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Dev\SapphireTest;
-use SilverStripe\Dev\TestOnly;
 use SilverStripe\Forms\FieldList;
 use SilverStripe\Forms\Form;
 use SilverStripe\ORM\DataList;
 use SilverStripe\ORM\DataObject;
+use SilverStripe\TagField\ReadonlyTagField;
 use SilverStripe\TagField\TagField;
 use SilverStripe\TagField\Tests\Stub\TagFieldTestBlogPost;
 use SilverStripe\TagField\Tests\Stub\TagFieldTestBlogTag;
@@ -342,4 +342,14 @@ class TagFieldTest extends SapphireTest
             $record->Tags()->first()->ID
         );
     }
+
+    /**
+     * Test read only fields are returned
+     */
+    public function testReadonlyTransformation()
+    {
+        $field = new TagField('Tags', '', TagFieldTestBlogTag::get());
+        $readOnlyField = $field->performReadonlyTransformation();
+        $this->assertEquals(ReadonlyTagField::class, get_class($readOnlyField));
+    }
 }