diff --git a/src/wp-includes/post-template.php b/src/wp-includes/post-template.php
index d5f839cf6d..c4050d9718 100644
--- a/src/wp-includes/post-template.php
+++ b/src/wp-includes/post-template.php
@@ -404,12 +404,20 @@ function post_class( $class = '', $post_id = null ) {
  * @return array Array of classes.
  */
 function get_post_class( $class = '', $post_id = null ) {
-	$post = get_post($post_id);
+	$post = get_post( $post_id );
 
 	$classes = array();
 
-	if ( empty($post) )
+	if ( $class ) {
+		if ( ! is_array( $class ) ) {
+			$class = preg_split( '#\s+#', $class );
+		}
+		$classes = array_map( 'esc_attr', $class );
+	}
+
+	if ( ! $post ) {
 		return $classes;
+	}
 
 	$classes[] = 'post-' . $post->ID;
 	if ( ! is_admin() )
@@ -466,13 +474,7 @@ function get_post_class( $class = '', $post_id = null ) {
 		}
 	}
 
-	if ( !empty($class) ) {
-		if ( !is_array( $class ) )
-			$class = preg_split('#\s+#', $class);
-		$classes = array_merge($classes, $class);
-	}
-
-	$classes = array_map('esc_attr', $classes);
+	$classes = array_map( 'esc_attr', $classes );
 
 	/**
 	 * Filter the list of CSS classes for the current post.
diff --git a/tests/phpunit/tests/post/getPostClass.php b/tests/phpunit/tests/post/getPostClass.php
index ff05972c1b..9329f21be4 100644
--- a/tests/phpunit/tests/post/getPostClass.php
+++ b/tests/phpunit/tests/post/getPostClass.php
@@ -44,6 +44,15 @@ class Tests_Post_GetPostClass extends WP_UnitTestCase {
 		$this->assertContains( 'wptests_tax-bar', $found );
 	}
 
+	/**
+	 * @ticket 22271
+	 */
+	public function test_with_custom_classes_and_no_post() {
+		$this->assertEquals( array(), get_post_class( '', null ) );
+		$this->assertEquals( array( 'foo' ), get_post_class( 'foo', null ) );
+		$this->assertEquals( array( 'foo', 'bar' ),  get_post_class( array( 'foo', 'bar' ), null ) );
+	}
+
 	/**
 	 * @group cache
 	 */