diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 2507ce10d8..0cd4681b28 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -692,13 +692,18 @@ function get_intermediate_image_sizes() {
  *
  * A mime icon for files, thumbnail or intermediate size for images.
  *
+ * The returned array contains four values: the URL of the attachment image src,
+ * the width of the image file, the height of the image file, and a boolean
+ * representing whether the returned array describes an intermediate (generated)
+ * image size or the original, full-sized upload.
+ *
  * @since 2.5.0
  *
  * @param int          $attachment_id Image attachment ID.
  * @param string|array $size          Optional. Registered image size to retrieve the source for or a flat
  *                                    array of height and width dimensions. Default 'thumbnail'.
  * @param bool         $icon          Optional. Whether the image should be treated as an icon. Default false.
- * @return false|array Returns an array (url, width, height), or false, if no image is available.
+ * @return false|array Returns an array (url, width, height, is_intermediate), or false, if no image is available.
  */
 function wp_get_attachment_image_src( $attachment_id, $size = 'thumbnail', $icon = false ) {
 	// get a thumbnail or intermediate image if there is one