diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 2f7dc1fca7..dee0af6817 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -1545,10 +1545,8 @@ function add_theme_support( $feature ) {
 			 * Merge post types with any that already declared their support
 			 * for post thumbnails.
 			 */
-			if ( is_array( $args[0] ) && is_array( $_wp_theme_features['post-thumbnails'][0] ) ) {
-				$post_types = array_unique( array_merge( $args[0], $_wp_theme_features['post-thumbnails'][0] ) );
-
-				$args = array( $post_types );
+			if ( is_array( $args[0] ) && isset( $_wp_theme_features['post-thumbnails'] ) ) {
+				$args[0] = array_unique( array_merge( $_wp_theme_features['post-thumbnails'][0], $args[0] ) );
 			}
 
 			break;
diff --git a/wp-includes/version.php b/wp-includes/version.php
index fdd54ed064..760298054d 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.6-alpha-37309';
+$wp_version = '4.6-alpha-37313';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.