diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 7c9312e49d..9a502b98b2 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -755,8 +755,8 @@ function wp_get_attachment_image_src( $attachment_id, $size = 'thumbnail', $icon
  * @since 2.5.0
  *
  * @param int          $attachment_id Image attachment ID.
- * @param string|array $size          Optional. Registered image size or flat array of height and width
- *                                    dimensions. Default 'thumbnail'.
+ * @param string|array $size          Optional. Image size. Accepts any valid image size, or an array of width
+ *                                    and height values in pixels (in that order). Default 'thumbnail'.
  * @param bool         $icon          Optional. Whether the image should be treated as an icon. Default false.
  * @param string|array $attr          Optional. Attributes for the image markup. Default empty.
  * @return string HTML img element or empty string on failure.