diff --git a/wp-includes/script-loader.php b/wp-includes/script-loader.php
index 4915c2ba98..6a3cf7d5e5 100644
--- a/wp-includes/script-loader.php
+++ b/wp-includes/script-loader.php
@@ -2470,7 +2470,7 @@ function script_concat_settings() {
 function wp_common_block_scripts_and_styles() {
 	global $current_screen;
 
-	if ( is_admin() && ! $current_screen->is_block_editor() ) {
+	if ( is_admin() && ( $current_screen instanceof WP_Screen ) && ! $current_screen->is_block_editor() ) {
 		return;
 	}
 
@@ -2504,7 +2504,7 @@ function wp_common_block_scripts_and_styles() {
 function wp_enqueue_registered_block_scripts_and_styles() {
 	global $current_screen;
 
-	$is_editor = ( is_admin() && $current_screen->is_block_editor() );
+	$is_editor = ( ( $current_screen instanceof WP_Screen ) && $current_screen->is_block_editor() );
 
 	$block_registry = WP_Block_Type_Registry::get_instance();
 	foreach ( $block_registry->get_all_registered() as $block_name => $block_type ) {
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 43ff5be959..b9b5fdb764 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44247';
+$wp_version = '5.1-alpha-44249';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.