Ticket #51182: 51182.diff

src/wp-admin/includes/class-theme-installer-skin.php

@@ -206 +206 @@
                 $all_themes         = wp_get_themes( array( 'errors' => null ) );
 
                 foreach ( $all_themes as $theme ) {
-                        if ( rtrim( $theme->get_stylesheet_directory(), '/' ) !== $folder ) {
+                    $stylesheet_dir = $theme->get_stylesheet_directory();
+                    $stylesheet_dir = str_replace( '\\', '/', $stylesheet_dir);
+                        if ( rtrim( $stylesheet_dir, '/' ) !== $folder ) {
                                 continue;
                         }