Index: src/wp-includes/media.php
===================================================================
--- src/wp-includes/media.php	(revision 35249)
+++ src/wp-includes/media.php	(working copy)
@@ -1003,7 +1003,7 @@
  * @return string|bool A valid source size value for use in a 'sizes' attribute or false.
  */
 function wp_get_attachment_image_sizes( $attachment_id, $size = 'medium', $args = null ) {
-
+	$img_width = 0;
 	// Try to get the image width from $args.
 	if ( is_array( $args ) && ! empty( $args['width'] ) ) {
 		$img_width = (int) $args['width'];