diff --git a/src/wp-includes/post.php b/src/wp-includes/post.php
index c7dcc13b8d..df509fd114 100644
--- a/src/wp-includes/post.php
+++ b/src/wp-includes/post.php
@@ -4159,12 +4159,14 @@ function wp_insert_post( $postarr, $wp_error = false, $fire_after_hooks = true )
 	 *
 	 * For new posts check the primitive capability, for updates check the meta capability.
 	 */
-	$post_type_object = get_post_type_object( $post_type );
+	if ( 'pending' === $post_status ) {
+		$post_type_object = get_post_type_object( $post_type );
 
-	if ( ! $update && 'pending' === $post_status && ! current_user_can( $post_type_object->cap->publish_posts ) ) {
-		$post_name = '';
-	} elseif ( $update && 'pending' === $post_status && ! current_user_can( 'publish_post', $post_ID ) ) {
-		$post_name = '';
+		if ( ! $update && $post_type_object && ! current_user_can( $post_type_object->cap->publish_posts ) ) {
+			$post_name = '';
+		} elseif ( $update && ! current_user_can( 'publish_post', $post_ID ) ) {
+			$post_name = '';
+		}
 	}
 
 	/*
diff --git a/tests/phpunit/tests/post.php b/tests/phpunit/tests/post.php
index 108e6ef4a6..e672dafdd7 100644
--- a/tests/phpunit/tests/post.php
+++ b/tests/phpunit/tests/post.php
@@ -501,6 +501,23 @@ class Tests_Post extends WP_UnitTestCase {
 		$this->assertStringContainsString( 'wptests_pt=' . $p, $post->guid );
 	}
 
+	/**
+	 * @ticket 55877
+	 * @covers ::wp_insert_post
+	 */
+	public function test_wp_insert_post_should_not_trigger_warning_for_pending_posts_with_unknown_cpt() {
+		$post_id = wp_insert_post(
+			array(
+				'post_title'  => 'title',
+				'post_type'   => 'unknown',
+				'post_status' => 'pending',
+			)
+		);
+
+		$this->assertIsNumeric( $post_id );
+		$this->assertGreaterThan( 0, $post_id );
+	}
+
 	/**
 	 * @ticket 20451
 	 */