diff --git a/app/config/errors.php b/app/config/errors.php
index 74e2de7db2..2b21ff48e2 100644
--- a/app/config/errors.php
+++ b/app/config/errors.php
@@ -541,9 +541,14 @@ return [
     ],
     Exception::DOMAIN_ALREADY_EXISTS => [
         'name' => Exception::DOMAIN_ALREADY_EXISTS,
-        'description' => 'A Domain with the requested ID already exists.',
+        'description' => 'The requested domain is currently in use by a project.',
         'code' => 409,
     ],
+    Exception::DOMAIN_FORBIDDEN => [
+        'name' => Exception::DOMAIN_FORBIDDEN,
+        'description' => 'The requested domain cannot be used as a custom domain.',
+        'code' => 403,
+    ],
     Exception::VARIABLE_NOT_FOUND => [
         'name' => Exception::VARIABLE_NOT_FOUND,
         'description' => 'Variable with the requested ID could not be found.',
diff --git a/app/controllers/api/projects.php b/app/controllers/api/projects.php
index 5fef7eab78..c7a85f0489 100644
--- a/app/controllers/api/projects.php
+++ b/app/controllers/api/projects.php
@@ -1191,9 +1191,12 @@ App::post('/v1/projects/:projectId/domains')
             throw new Exception(Exception::PROJECT_NOT_FOUND);
         }
 
+        if ($domain === App::getEnv('_APP_DOMAIN', '') || $domain === App::getEnv('_APP_DOMAIN_TARGET', '')) {
+            throw new Exception(Exception::DOMAIN_FORBIDDEN);
+        }
+
         $document = $dbForConsole->findOne('domains', [
-            Query::equal('domain', [$domain]),
-            Query::equal('projectInternalId', [$project->getInternalId()]),
+            Query::equal('domain', [$domain])
         ]);
 
         if ($document && !$document->isEmpty()) {
@@ -1391,6 +1394,10 @@ App::delete('/v1/projects/:projectId/domains/:domainId')
             throw new Exception(Exception::DOMAIN_NOT_FOUND);
         }
 
+        if ($domain->getAttribute('domain') === App::getEnv('_APP_DOMAIN', '') || $domain->getAttribute('domain') === App::getEnv('_APP_DOMAIN_TARGET', '')) {
+            throw new Exception(Exception::DOMAIN_FORBIDDEN);
+        }
+
         $dbForConsole->deleteDocument('domains', $domain->getId());
 
         $dbForConsole->deleteCachedDocument('projects', $project->getId());
diff --git a/src/Appwrite/Extend/Exception.php b/src/Appwrite/Extend/Exception.php
index 8ee0dca0c6..ecf6e17c1f 100644
--- a/src/Appwrite/Extend/Exception.php
+++ b/src/Appwrite/Extend/Exception.php
@@ -177,6 +177,7 @@ class Exception extends \Exception
     /** Domain */
     public const DOMAIN_NOT_FOUND                  = 'domain_not_found';
     public const DOMAIN_ALREADY_EXISTS             = 'domain_already_exists';
+    public const DOMAIN_FORBIDDEN                  = 'domain_forbidden';
     public const DOMAIN_VERIFICATION_FAILED        = 'domain_verification_failed';
 
     protected $type = '';