diff --git a/src/wp-includes/class-wp.php b/src/wp-includes/class-wp.php
index 0a0a501ee0..67985c147b 100644
--- a/src/wp-includes/class-wp.php
+++ b/src/wp-includes/class-wp.php
@@ -410,8 +410,12 @@ class WP {
 	 * @since 2.0.0
 	 * @since 4.4.0 `X-Pingback` header is added conditionally for single posts that allow pings.
 	 * @since 6.1.0 Runs after posts have been queried.
+	 *
+	 * @global WP_Query $wp_query WordPress Query object.
 	 */
 	public function send_headers() {
+		global $wp_query;
+
 		$headers       = array();
 		$status        = null;
 		$exit_required = false;
diff --git a/tests/phpunit/tests/wp/sendHeaders.php b/tests/phpunit/tests/wp/sendHeaders.php
index cc956409ef..84feb74d1d 100644
--- a/tests/phpunit/tests/wp/sendHeaders.php
+++ b/tests/phpunit/tests/wp/sendHeaders.php
@@ -19,4 +19,19 @@ class Tests_WP_SendHeaders extends WP_UnitTestCase {
 
 		$this->go_to( home_url() );
 	}
+
+	/**
+	 * @ticket 56840
+	 */
+	public function test_send_headers_sets_x_pingback_for_single_posts_that_allow_pings() {
+		add_action(
+			'wp_headers',
+			function ( $headers ) {
+				$this->assertArrayHasKey( 'X-Pingback', $headers );
+			}
+		);
+
+		$post_id = self::factory()->post->create();
+		$this->go_to( get_permalink( $post_id ) );
+	}
 }