diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 75bde9a2c9..34fbeb7bda 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -337,7 +337,8 @@ function get_image_tag( $id, $alt, $title, $align, $size = 'medium' ) {
 	 * @param string $class CSS class name or space-separated list of classes.
 	 * @param int    $id    Attachment ID.
 	 * @param string $align Part of the class name for aligning the image.
-	 * @param string $size  Optional. Default is 'medium'.
+	 * @param string $size  Size of image. Image size or array of width and height values (in that order).
+	 *                      Default 'medium'.
 	 */
 	$class = apply_filters( 'get_image_tag_class', $class, $id, $align, $size );