diff --git a/README.md b/README.md
index ee76745..ccf9369 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # [misdirection](https://packagist.org/packages/nglasl/silverstripe-misdirection)
 
-_The current release is **2.2.26**_
+_The current release is **2.3.0**_
 
 > A module for SilverStripe which will allow both simple and regular expression link redirections based on customisable mappings, either hooking into a page not found or replacing the default automated URL handling.
 
diff --git a/code/dataobjects/LinkMapping.php b/code/dataobjects/LinkMapping.php
index 8cf202d..0c7608f 100644
--- a/code/dataobjects/LinkMapping.php
+++ b/code/dataobjects/LinkMapping.php
@@ -272,10 +272,6 @@ public function getCMSFields() {
 		return $fields;
 	}
 
-	/**
-	 *	Confirm that the current link mapping is valid.
-	 */
-
 	public function validate() {
 
 		$result = parent::validate();
diff --git a/code/extensions/SiteTreeMisdirectionExtension.php b/code/extensions/SiteTreeMisdirectionExtension.php
index 4e69921..f3945ba 100644
--- a/code/extensions/SiteTreeMisdirectionExtension.php
+++ b/code/extensions/SiteTreeMisdirectionExtension.php
@@ -15,10 +15,6 @@ class SiteTreeMisdirectionExtension extends DataExtension {
 		'VanityMapping' => 'LinkMapping'
 	);
 
-	/**
-	 *	Display the vanity mapping fields.
-	 */
-
 	public function updateSettingsFields($fields) {
 
 		$fields->addFieldToTab('Root.Misdirection', HeaderField::create(
@@ -42,6 +38,33 @@ public function updateSettingsFields($fields) {
 		$this->owner->extend('updateSiteTreeMisdirectionExtensionSettingsFields', $fields);
 	}
 
+	public function validate(ValidationResult $result) {
+
+		// Retrieve the vanity mapping URL, where this is only possible using the POST variable.
+
+		$vanityURL = (!Controller::has_curr() || is_null($controller = Controller::curr()) || is_null($URL = $controller->getRequest()->postVar('VanityURL'))) ? $this->owner->VanityMapping()->MappedLink : $URL;
+
+		// Determine whether another vanity mapping already exists.
+		
+		$existing = LinkMapping::get()->filter(array(
+			'MappedLink' => $vanityURL,
+			'RedirectType' => 'Page',
+			'RedirectPageID:not' => array(
+				0,
+				$this->owner->ID
+			)
+		))->first();
+		if($result->valid() && $existing && ($page = $existing->getRedirectPage())) {
+			$link = Controller::join_links(CMSPageSettingsController::singleton()->Link('show'), $page->ID);
+			$result->error('Vanity URL already exists!');
+		}
+
+		// Allow extension.
+
+		$this->owner->extend('validateSiteTreeMisdirectionExtension', $result);
+		return $result;
+	}
+
 	/**
 	 *	Update the corresponding vanity mapping.
 	 */
diff --git a/composer.json b/composer.json
index 1ac3664..4cf25d0 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,7 @@
 	"extra": {
 		"installer-name": "misdirection",
 		"branch-alias": {
-			"dev-master": "2.2.x-dev"
+			"dev-master": "2.3.x-dev"
 		},
 		"screenshots": [
 			"https://raw.githubusercontent.com/nglasl/silverstripe-misdirection/master/images/misdirection-testing.png"