diff --git a/wp-admin/includes/media.php b/wp-admin/includes/media.php
index f22504d9c3..f08cbfa9e6 100644
--- a/wp-admin/includes/media.php
+++ b/wp-admin/includes/media.php
@@ -116,11 +116,11 @@ function get_image_send_to_editor($id, $alt, $title, $align, $url='', $rel = fal
 
 function _wp_post_thumbnail_html( $thumbnail_id = NULL ) {
 	if ( $thumbnail_id && get_post( $thumbnail_id ) ) {
-		$thumbnail_html = wp_get_attachment_image($thumbnail_id, 'thumbnail');
+		$thumbnail_html = wp_get_attachment_image($thumbnail_id, array( 266, 266 ) );
 		if ( !empty( $thumbnail_html ) )
-			return '<a href="#" id="cws-post-thumbnail" onclick="jQuery(\'#add_image\').click();return false;">' . $thumbnail_html . '</a>';
+			return apply_filters( 'admin_post_thumbnail_html', '<a href="#" id="cws-post-thumbnail" onclick="jQuery(\'#add_image\').click();return false;">' . $thumbnail_html . '</a>' );
 	}
-	return '<a href="#" id="cws-post-thumbnail" onclick="jQuery(\'#add_image\').click();return false;">' . esc_html__( 'Set thumbnail' ) . '</a>';
+	return apply_filters( 'admin_post_thumbnail_html', '<a href="#" id="cws-post-thumbnail" onclick="jQuery(\'#add_image\').click();return false;">' . esc_html__( 'Set thumbnail' ) . '</a>' );
 }
 
 function post_thumbnail_meta_box() {