diff --git a/wp-admin/includes/class-theme-installer-skin.php b/wp-admin/includes/class-theme-installer-skin.php
index 16e99332a6..c6d0900abe 100644
--- a/wp-admin/includes/class-theme-installer-skin.php
+++ b/wp-admin/includes/class-theme-installer-skin.php
@@ -206,7 +206,9 @@ class Theme_Installer_Skin extends WP_Upgrader_Skin {
 		$all_themes         = wp_get_themes( array( 'errors' => null ) );
 
 		foreach ( $all_themes as $theme ) {
-			if ( rtrim( $theme->get_stylesheet_directory(), '/' ) !== $folder ) {
+			$stylesheet_dir = wp_normalize_path( $theme->get_stylesheet_directory() );
+
+			if ( rtrim( $stylesheet_dir, '/' ) !== $folder ) {
 				continue;
 			}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index fe385288bd..121cae7d6d 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-alpha-48912';
+$wp_version = '5.6-alpha-48913';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.