diff --git a/wp-admin/includes/ajax-actions.php b/wp-admin/includes/ajax-actions.php
index e3016258cd..cc9fa432fc 100644
--- a/wp-admin/includes/ajax-actions.php
+++ b/wp-admin/includes/ajax-actions.php
@@ -3405,7 +3405,7 @@ function wp_ajax_update_theme() {
 		) );
 	}
 
-	$stylesheet = sanitize_key( wp_unslash( $_POST['slug'] ) );
+	$stylesheet = preg_replace( '/[^A-z0-9_\-]/', '', wp_unslash( $_POST['slug'] ) );
 	$status     = array(
 		'update'     => 'theme',
 		'slug'       => $stylesheet,
@@ -3490,7 +3490,7 @@ function wp_ajax_delete_theme() {
 		) );
 	}
 
-	$stylesheet = sanitize_key( wp_unslash( $_POST['slug'] ) );
+	$stylesheet = preg_replace( '/[^A-z0-9_\-]/', '', wp_unslash( $_POST['slug'] ) );
 	$status     = array(
 		'delete' => 'theme',
 		'slug'   => $stylesheet,
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 3899d13b45..5a80fd876a 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-alpha-38709';
+$wp_version = '4.7-alpha-38710';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.