diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 9a502b98b2..19c6ffa38a 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -801,7 +801,8 @@ function wp_get_attachment_image($attachment_id, $size = 'thumbnail', $icon = fa
 		 *
 		 * @param array        $attr       Attributes for the image markup.
 		 * @param WP_Post      $attachment Image attachment post.
-		 * @param string|array $size       Requested size.
+		 * @param string|array $size       Requested size. Image size or array of width and height values
+		 *                                 (in that order). Default 'thumbnail'.
 		 */
 		$attr = apply_filters( 'wp_get_attachment_image_attributes', $attr, $attachment, $size );
 		$attr = array_map( 'esc_attr', $attr );