Index: src/wp-includes/media.php
===================================================================
--- src/wp-includes/media.php	(revision 28696)
+++ src/wp-includes/media.php	(working copy)
@@ -2601,7 +2601,8 @@
 		$response['uploadedToTitle'] = $post_parent->post_title ? $post_parent->post_title : __( '(No title)' );
 	}
 
-	$bytes = filesize( get_attached_file( $attachment->ID ) );
+	$file = get_attached_file( $attachment->ID );
+	$bytes = ( file_exists( $file ) ) ? filesize( $file ) : 0;
 	$response['filesizeInBytes'] = $bytes;
 	$response['filesizeHumanReadable'] = size_format( $bytes );