Index: src/wp-admin/includes/class-wp-upgrader.php
===================================================================
--- src/wp-admin/includes/class-wp-upgrader.php	(revision 25761)
+++ src/wp-admin/includes/class-wp-upgrader.php	(working copy)
@@ -1507,7 +1507,7 @@
 		// Search all directories we've found for evidence of version control.
 		foreach ( $vcs_dirs as $vcs_dir ) {
 			foreach ( $check_dirs as $check_dir ) {
-				if ( $checkout = is_dir( rtrim( $check_dir, '\\/' ) . "/$vcs_dir" ) )
+				if ( $checkout = @is_dir( rtrim( $check_dir, '\\/' ) . "/$vcs_dir" ) )
 					break 2;
 			}
 		}