diff --git a/src/wp-includes/post.php b/src/wp-includes/post.php
index 81cd12a12e..39eb6a35e9 100644
--- a/src/wp-includes/post.php
+++ b/src/wp-includes/post.php
@@ -3720,7 +3720,7 @@ function wp_unique_post_slug( $slug, $post_ID, $post_status, $post_type, $post_p
 			$suffix = 2;
 			do {
 				$alt_post_name = _truncate_post_slug( $slug, 200 - ( strlen( $suffix ) + 1 ) ) . "-$suffix";
-				$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $alt_post_name, $post_ID, $post_parent ) );
+				$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $alt_post_name, $post_type, $post_ID, $post_parent ) );	
 				$suffix++;
 			} while ( $post_name_check );
 			$slug = $alt_post_name;
diff --git a/tests/phpunit/tests/post.php b/tests/phpunit/tests/post.php
index 94f6817463..0962f92bbd 100644
--- a/tests/phpunit/tests/post.php
+++ b/tests/phpunit/tests/post.php
@@ -1017,6 +1017,67 @@ class Tests_Post extends WP_UnitTestCase {
 		_unregister_post_type( 'post-type-2' );
 	}
 
+	/**
+	 * @ticket 30339
+	 */
+	function test_wp_unique_post_slug_with_hierarchy() {
+		register_post_type( 'post-type-1', array( 'hierarchical' => true ) );
+
+		$args = array(
+			'post_type' => 'post-type-1',
+			'post_name' => 'some-slug',
+			'post_status' => 'publish',
+		);
+		$one = $this->factory->post->create( $args );
+		$args['post_name'] = 'some-slug-2';
+		$two = $this->factory->post->create( $args );
+
+		$this->assertEquals( 'some-slug', get_post( $one )->post_name );
+		$this->assertEquals( 'some-slug-2', get_post( $two )->post_name );
+
+		$this->assertEquals( 'some-slug-3', wp_unique_post_slug( 'some-slug', 0, 'publish', 'post-type-1', 0 ) );
+
+		_unregister_post_type( 'post-type-1' );
+	}
+
+	/**
+	 * @ticket 18962
+	 */
+	function test_wp_unique_post_slug_with_hierarchy_and_attachments() {
+		register_post_type( 'post-type-1', array( 'hierarchical' => true ) );
+
+		$args = array(
+			'post_type' => 'post-type-1',
+			'post_name' => 'some-slug',
+			'post_status' => 'publish',
+		);
+		$one = $this->factory->post->create( $args );
+
+		$args = array(
+			'post_mime_type' => 'image/jpeg',
+			'post_type' => 'attachment',
+			'post_name' => 'image'
+		);
+		$attachment = $this->factory->attachment->create_object( 'image.jpg', $one, $args );
+
+		$args = array(
+			'post_type' => 'post-type-1',
+			'post_name' => 'image',
+			'post_status' => 'publish',
+			'post_parent' => $one
+		);
+		$two = $this->factory->post->create( $args );
+
+		$this->assertEquals( 'some-slug', get_post( $one )->post_name );
+		$this->assertEquals( 'image', get_post( $attachment )->post_name );
+		$this->assertEquals( 'image-2', get_post( $two )->post_name );
+
+		// 'image' can be a child of image-2
+		$this->assertEquals( 'image', wp_unique_post_slug( 'image', 0, 'publish', 'post-type-1', $two ) );
+
+		_unregister_post_type( 'post-type-1' );
+	}
+
 	/**
 	 * @ticket 21212
 	 */