diff --git a/inc/manager.php b/inc/manager.php
index cb3cea3f..1fa34eae 100644
--- a/inc/manager.php
+++ b/inc/manager.php
@@ -393,7 +393,7 @@ public static function is_ajax_request() {
 		if ( ! wp_doing_ajax() ) {
 			return false;
 		}
-		if ( isset( $_REQUEST['action'] ) && strpos( $_REQUEST['action'], 'wpmdb' ) !== false ) {
+		if ( isset( $_REQUEST['action'] ) && is_string( $_REQUEST['action'] ) && strpos( $_REQUEST['action'], 'wpmdb' ) !== false ) {
 			return false;
 		}
 
diff --git a/tests/test-ajax-request-detection.php b/tests/test-ajax-request-detection.php
new file mode 100644
index 00000000..914af0af
--- /dev/null
+++ b/tests/test-ajax-request-detection.php
@@ -0,0 +1,104 @@
+<?php
+/**
+ * WordPress unit tests for AJAX request detection.
+ *
+ * @package     Optimole-WP
+ * @subpackage  Tests
+ * @copyright   Copyright (c) 2026, ThemeIsle
+ * @license     http://opensource.org/licenses/gpl-2.0.php GNU Public License
+ */
+
+/**
+ * Class Test_Ajax_Request_Detection.
+ */
+class Test_Ajax_Request_Detection extends WP_UnitTestCase {
+
+	/**
+	 * Whether the action key was present before the test.
+	 *
+	 * @var bool
+	 */
+	private $had_action = false;
+
+	/**
+	 * The original action value, when there was one.
+	 *
+	 * @var mixed
+	 */
+	private $original_action = null;
+
+	public function setUp(): void {
+		parent::setUp();
+
+		$this->had_action = isset( $_REQUEST['action'] );
+
+		if ( $this->had_action ) {
+			$this->original_action = $_REQUEST['action'];
+		}
+
+		// DOING_AJAX cannot be defined per test, the filter is the supported way in.
+		add_filter( 'wp_doing_ajax', '__return_true' );
+
+		wp_set_current_user( 0 );
+	}
+
+	public function tearDown(): void {
+		remove_filter( 'wp_doing_ajax', '__return_true' );
+
+		if ( $this->had_action ) {
+			$_REQUEST['action'] = $this->original_action;
+		} else {
+			unset( $_REQUEST['action'] );
+		}
+
+		$this->had_action      = false;
+		$this->original_action = null;
+
+		parent::tearDown();
+	}
+
+	/**
+	 * An array-valued action, i.e. `action[]=wpmdb`, must not fatal.
+	 */
+	public function test_array_action_does_not_fatal() {
+		$_REQUEST['action'] = [ 'wpmdb' ];
+
+		$this->assertTrue( Optml_Manager::is_ajax_request() );
+	}
+
+	/**
+	 * A nested array action is handled the same way.
+	 */
+	public function test_nested_array_action_does_not_fatal() {
+		$_REQUEST['action'] = [ 'a' => [ 'wpmdb' ] ];
+
+		$this->assertTrue( Optml_Manager::is_ajax_request() );
+	}
+
+	/**
+	 * WP Migrate DB requests stay excluded, the guarantee from 02df0774.
+	 */
+	public function test_wpmdb_action_still_excluded() {
+		$_REQUEST['action'] = 'wpmdb_verify_connection_to_remote_site';
+
+		$this->assertFalse( Optml_Manager::is_ajax_request() );
+	}
+
+	/**
+	 * An unrelated AJAX action is still treated as a replaceable request.
+	 */
+	public function test_unrelated_action_is_ajax_request() {
+		$_REQUEST['action'] = 'woocommerce_get_refreshed_fragments';
+
+		$this->assertTrue( Optml_Manager::is_ajax_request() );
+	}
+
+	/**
+	 * A request with no action at all is still treated as a replaceable request.
+	 */
+	public function test_missing_action_is_ajax_request() {
+		unset( $_REQUEST['action'] );
+
+		$this->assertTrue( Optml_Manager::is_ajax_request() );
+	}
+}