diff --git a/src/Slug.php b/src/Slug.php
index 9f19ebe..ec238d2 100644
--- a/src/Slug.php
+++ b/src/Slug.php
@@ -3,12 +3,12 @@
 namespace Nightjar\Slug;
 
 use InvalidArgumentException;
-use UnexpectedValueException;
-use SilverStripe\ORM\DataObject;
+use SilverStripe\Control\Controller;
 use SilverStripe\Forms\FieldList;
 use SilverStripe\ORM\DataExtension;
-use SilverStripe\Control\Controller;
+use SilverStripe\ORM\DataObject;
 use SilverStripe\View\Parsers\URLSegmentFilter;
+use UnexpectedValueException;
 
 /**
  * Adds a 'url slug' property to DataObject classes, in order for them to be able to be loaded via a URL
@@ -76,8 +76,8 @@ class Slug extends DataExtension
     /**
      * Apply extension with configurable defaults
      *
-     * @param string  $fieldToSlug   The field on the owner to base the URL Slug from - defaults to 'Title'
-     * @param string  $relationName  Optional name of the has_one relationship to the owner's parent class/Page
+     * @param string $fieldToSlug The field on the owner to base the URL Slug from - defaults to 'Title'
+     * @param string $relationName Optional name of the has_one relationship to the owner's parent class/Page
      * @param boolean $enforceParity true to alter the URLSlug whenever the $fieldToSlug changes value (default: false)
      */
     public function __construct($fieldToSlug = 'Title', $relationName = null, $enforceParity = false)
@@ -132,72 +132,104 @@ public function setSlugActive($active)
     }
 
     /**
-     * Generate a url slug segment
-     *
-     * @param  boolean $forceRegeneration
-     * @return string
+     * Check for collisions, if we need to update the slug and
+     * update the model with the confirmedsafe value before writing
      */
-    public function getSlug($forceRegeneration = false)
+    public function onBeforeWrite()
     {
-        $owner = $this->getOwner();
-        $field = $this->fieldToSlug;
-        $unfilteredSlug = $owner->URLSlug;
-        if (!$unfilteredSlug || $forceRegeneration) {
-            $unfilteredSlug = $owner->$field;
+        if ($this->slugIsOutdated()) {
+            $this->updateSlug();
+        } elseif ($this->slugHasChanged()) {
+            // enforceParity is set, and the slug has changed... but the
+            // field to slug has not. We need to reset to keep parity.
+            // Ideally we could do this via the $original property through
+            // {@see DataObject::getChangedFields}, however the returned
+            // 'before' value for a changed field is unreliable :(
+            // https://github.com/silverstripe/silverstripe-framework/issues/8443
+            throw new UnexpectedValueException(
+                'URLSlug has been updated independently of the tracked field, ' .
+                'but this has been disabled via Slug::enforceParity'
+            );
         }
-        return URLSegmentFilter::create()->filter($unfilteredSlug);
     }
 
     /**
-     * Check for collisions, iff we need to update the slug and
-     * upate the model with the confirmedsafe value before writing
+     * Helper to decide if a slug is outdated
+     *
+     * @return bool
      */
-    public function onBeforeWrite()
+    public function slugIsOutdated(): bool
     {
         $owner = $this->getOwner();
-        $slugHasChanged = $owner->isChanged('URLSlug');
+        $slugHasChanged = $this->slugHasChanged();
         $fieldToSlugHasChanged = $owner->isChanged($this->fieldToSlug);
-        $updateSlug = (
+        $relationHasChanged = $this->relationName && $owner->isChanged($this->relationName . 'ID');
+
+        return (
             empty($owner->URLSlug)
             || ($this->enforceParity && $fieldToSlugHasChanged)
             || (!$this->enforceParity && $slugHasChanged)
+            || $relationHasChanged
         );
+    }
 
-        if ($updateSlug) {
-            $owner->URLSlug = $this->getSlug($this->enforceParity);
-
-            $collisionList = DataObject::get(get_class($owner))->exclude('ID', $owner->ID);
-            $filter = ['URLSlug' => $owner->URLSlug];
-            if ($this->relationName) {
-                $parentIDField = $this->relationName . 'ID';
-                $filter[$parentIDField] = $owner->$parentIDField;
-                // Also handle polymorphic relationships
-                $parentClassName = DataObject::getSchema()->hasOneComponent(get_class($owner), $this->relationName);
-                if ($parentClassName === DataObject::class) {
-                    $parentClassField = $this->relationName . 'Class';
-                    $filter[$parentClassField] = $owner->$parentClassField;
-                }
-            }
+    /**
+     * the actual logic for updating the slug and fix collisions with other slugs that have the same parent
+     */
+    public function updateSlug(): void
+    {
+        $owner = $this->getOwner();
+        $owner->URLSlug = $this->getSlug($this->enforceParity);
 
-            $count = 1;
-            while ($collisionList->filter($filter)->exists()) {
-                $owner->URLSlug = $owner->URLSlug . $count++;
-                $filter['URLSlug'] = $owner->URLSlug;
+        $collisionList = DataObject::get(get_class($owner))->exclude('ID', $owner->ID);
+        $filter = ['URLSlug' => $owner->URLSlug];
+
+        if ($this->relationName) {
+            $parentIDField = $this->relationName . 'ID';
+            $filter[$parentIDField] = $owner->$parentIDField;
+            // Also handle polymorphic relationships
+            $parentClassName = DataObject::getSchema()->hasOneComponent(get_class($owner), $this->relationName);
+            if ($parentClassName === DataObject::class) {
+                $parentClassField = $this->relationName . 'Class';
+                $filter[$parentClassField] = $owner->$parentClassField;
             }
-        } elseif ($slugHasChanged) {
-            // enforceParity is set, and the slug has changed... but the
-            // field to slug has not. We need to reset to keep parity.
-            // Ideally we could do this via the $original property through
-            // {@see DataObject::getChangedFields}, however the returned
-            // 'before' value for a changed field is unreliable :(
-            // https://github.com/silverstripe/silverstripe-framework/issues/8443
-            throw new UnexpectedValueException(
-                'URLSlug has been updated independently of the tracked field, ' .
-                'but this has been disabled via Slug::enforceParity'
-            );
+        }
+
+        $count = 1;
+        $origSlug = $owner->URLSlug;
+        while ($collisionList->filter($filter)->exists()) {
+            $owner->URLSlug = implode('-', [$origSlug, $count++]);
+            $filter['URLSlug'] = $owner->URLSlug;
         }
     }
 
+    /**
+     * Generate a url slug segment
+     *
+     * @param boolean $forceRegeneration
+     * @return string
+     */
+    public function getSlug($forceRegeneration = false)
+    {
+        $owner = $this->getOwner();
+        $field = $this->fieldToSlug;
+        $unfilteredSlug = $owner->URLSlug;
+        if (!$unfilteredSlug || $forceRegeneration) {
+            $unfilteredSlug = $owner->$field;
+        }
+        return URLSegmentFilter::create()->filter($unfilteredSlug);
+    }
+
+    /**
+     * Helper to decide if the slug field has changed
+     *
+     * @return bool
+     */
+    public function slugHasChanged(): bool
+    {
+        return $this->owner->isChanged('URLSlug');
+    }
+
     public function updateCMSFields(FieldList $fields)
     {
         if ($this->enforceParity) {
@@ -218,7 +250,7 @@ public function Link($action = null)
         $link = null;
         $owner = $this->getOwner();
         $action = ($action) ? Controller::join_links($owner->URLSlug, $action) : $owner->URLSlug;
-        
+
         $relationName = $this->relationName;
         if ($relationName && ($parent = $owner->$relationName()) && $parent->hasMethod('Link')) {
             $link = $parent->Link($action);
@@ -230,46 +262,46 @@ public function Link($action = null)
     }
 
     /**
-     * Returns true if this is the slugged object being used to handle this request.
+     * Return "link" or "section" depending on if this is the current viewing object.
+     * {@see isCurrent}
      *
-     * @return boolean
+     * @return string
      */
-    public function isCurrent()
+    public function LinkOrCurrent()
     {
-        return $this->active === self::ACTIVE_CURRENT;
+        return $this->isCurrent() ? 'current' : 'link';
     }
 
     /**
-     * Check if this slugged object is in the currently active section
-     * (i.e. it, or one of its children is currently being viewed).
+     * Returns true if this is the slugged object being used to handle this request.
      *
      * @return boolean
      */
-    public function isSection()
+    public function isCurrent()
     {
-        return $this->isCurrent() || ($this->active === self::ACTIVE_SECTION);
+        return $this->active === self::ACTIVE_CURRENT;
     }
 
     /**
-     * Return "link" or "section" depending on if this is the current viewing object.
-     * {@see isCurrent}
+     * Return "link" or "section" depending on if this is the current section.
+     * {@see isSection}
      *
      * @return string
      */
-    public function LinkOrCurrent()
+    public function LinkOrSection()
     {
-        return $this->isCurrent() ? 'current' : 'link';
+        return $this->isSection() ? 'section' : 'link';
     }
 
     /**
-     * Return "link" or "section" depending on if this is the current section.
-     * {@see isSection}
+     * Check if this slugged object is in the currently active section
+     * (i.e. it, or one of its children is currently being viewed).
      *
-     * @return string
+     * @return boolean
      */
-    public function LinkOrSection()
+    public function isSection()
     {
-        return $this->isSection() ? 'section' : 'link';
+        return $this->isCurrent() || ($this->active === self::ACTIVE_SECTION);
     }
 
     /**
diff --git a/tests/SlugHandlerTest.php b/tests/SlugHandlerTest.php
index 4beb108..27bb0d9 100644
--- a/tests/SlugHandlerTest.php
+++ b/tests/SlugHandlerTest.php
@@ -23,29 +23,6 @@ class SlugHandlerTest extends FunctionalTest
         Journalist::class,
     ];
 
-    /**
-     * By all accounts this should be setUpBeforeClass... but it is too coarse a call to achieve getting
-     * Journalist.URLSlug into the database (modifying Conifg before calling parent::setUpBeforeClass is
-     * too soon, and calling after parent;:setUpBeforeClass is too late!). So we must hijack a call from
-     * within setUpBeforeClass to allow for this. This is the only viable option!
-     *
-     * The reason for this is because we cannot define TestOnly yaml configuration like we can with php
-     * fixture classes, and here we are also testing defining a service to apply the extension works.
-     * This is important for e.g. backwards compatiblity aliases
-     */
-    public static function getExtraDataObjects()
-    {
-        $config = Config::modify();
-        $config->set(Injector::class, 'JournalistSlug', [
-            'class' => Slug::class,
-            'constructor' => ['Name', 'NewsPages'],
-        ]);
-        $config->merge(Journalist::class, 'extensions', ['JournalistSlug']);
-
-        // Do what we actually came here for
-        return parent::getExtraDataObjects();
-    }
-
     protected function setUp()
     {
         parent::setUp();
diff --git a/tests/SlugTest.php b/tests/SlugTest.php
index b1adbe0..fc1d8bf 100644
--- a/tests/SlugTest.php
+++ b/tests/SlugTest.php
@@ -2,35 +2,31 @@
 
 namespace Nightjar\Slug\Tests;
 
-use Nightjar\Slug\Slug;
 use InvalidArgumentException;
-use UnexpectedValueException;
-use SilverStripe\Dev\SapphireTest;
-use SilverStripe\Core\Config\Config;
+use Nightjar\Slug\Slug;
 use Nightjar\Slug\Tests\Stubs\Article;
 use Nightjar\Slug\Tests\Stubs\Blitzem;
-use Nightjar\Slug\Tests\Stubs\NewsPage;
-use SilverStripe\Core\Injector\Injector;
 use Nightjar\Slug\Tests\Stubs\Journalist;
+use Nightjar\Slug\Tests\Stubs\NewsPage;
+use SilverStripe\Core\Config\Config;
+use SilverStripe\Dev\SapphireTest;
+use UnexpectedValueException;
 
 class SlugTest extends SapphireTest
 {
-    protected $usesTransactions = false;
-
     protected static $fixture_file = 'SlugTest.yml';
-
     protected static $extra_dataobjects = [
         Article::class,
         Blitzem::class,
         NewsPage::class,
         Journalist::class,
     ];
-
     protected static $required_extensions = [
         Journalist::class => [
             Slug::class
         ]
     ];
+    protected $usesTransactions = false;
 
     public function testGettingSlug()
     {
@@ -58,13 +54,6 @@ public function testCannotAssociateToInvalidRelationshipType()
 
     public function testSlugsWillSetAndSanitiseOnSave()
     {
-        $config = Config::modify();
-        $config->set(Injector::class, 'JournalistSlug', [
-            'class' => Slug::class,
-            'constructor' => ['Name', 'NewsPages'],
-        ]);
-        $config->merge(Journalist::class, 'extensions', ['JournalistSlug']);
-
         $journo = Journalist::create();
         $journo->update(['Name' => 'Ash Katchum!'])->extend('onBeforeWrite');
         $this->assertEquals('ash-katchum', $journo->URLSlug, 'initial write should sanitise');
@@ -76,7 +65,7 @@ public function testSlugsWillSetAndSanitiseOnSave()
     public function testSlugKeepsParity()
     {
         $newArticle = Article::create();
-        
+
         $newArticle->update(['Title' => 'Second News'])->fakeWrite();
         $this->assertEquals('second-news', $newArticle->URLSlug);
 
@@ -99,8 +88,35 @@ public function testSlugCollisionsCorrectThemselves()
             'Title' => 'First news',
             'ParentID' => $newsPage->ID,
         ]);
-        $newArticle->extend('onBeforeWrite');
-        $this->assertEquals('first-news1', $newArticle->URLSlug);
+        $newArticle->write();
+        $this->assertEquals('first-news-1', $newArticle->URLSlug);
+        $this->assertEquals('First news', $newArticle->Title);
+
+        $anotherArticle = Article::create()->update([
+            'Title' => 'First news',
+            'ParentID' => $newsPage->ID,
+        ]);
+        $anotherArticle->write();
+        $this->assertEquals('first-news-2', $anotherArticle->URLSlug);
+        $this->assertEquals('First news', $anotherArticle->Title);
+    }
+
+    public function testSlugCollisionFixesItselfWhenParentChanges()
+    {
+        $newsPage = $this->objFromFixture(NewsPage::class, 'holder');
+        $newArticle = Article::create()->update([
+            'Title' => 'First news',
+            'ParentID' => 0,
+        ]);
+        $newArticle->write();
+        $this->assertEquals('first-news', $newArticle->URLSlug,
+            'Slug doesn\'t need to be fixed when objects have different parents');
+        $this->assertEquals('First news', $newArticle->Title);
+
+        $newArticle->ParentID = $newsPage->ID;
+        $newArticle->write();
+        $this->assertEquals('first-news-1', $newArticle->URLSlug,
+            'Slug should fix when it collides with a slug in a new parent');
         $this->assertEquals('First news', $newArticle->Title);
     }
 
diff --git a/tests/Stubs/Journalist.php b/tests/Stubs/Journalist.php
index 5a83081..c8b9f08 100644
--- a/tests/Stubs/Journalist.php
+++ b/tests/Stubs/Journalist.php
@@ -2,6 +2,7 @@
 
 namespace Nightjar\Slug\Tests\Stubs;
 
+use Nightjar\Slug\Slug;
 use SilverStripe\Dev\TestOnly;
 use SilverStripe\ORM\DataObject;
 
@@ -16,4 +17,8 @@ class Journalist extends DataObject implements TestOnly
     private static $has_one = [
         'NewsPages' => NewsPage::class
     ];
+
+    private static $extensions = [
+        Slug::class . '("Name", "NewsPages")'
+    ];
 }