Index: src/wp-includes/class-wp-image-editor.php
===================================================================
--- src/wp-includes/class-wp-image-editor.php	(revision 38247)
+++ src/wp-includes/class-wp-image-editor.php	(working copy)
@@ -376,8 +376,8 @@
 			$suffix = $this->get_suffix();
 
 		$info = pathinfo( $this->file );
-		$dir  = $info['dirname'];
-		$ext  = $info['extension'];
+		$dir  = pathinfo( $this->file, PATHINFO_DIRNAME );
+		$ext  = pathinfo( $this->file, PATHINFO_EXTENSION );
 
 		$name = wp_basename( $this->file, ".$ext" );
 		$new_ext = strtolower( $extension ? $extension : $ext );