diff --git a/wp-includes/theme-previews.php b/wp-includes/theme-previews.php
index d9325ddbf3..e8e4a6a8c8 100644
--- a/wp-includes/theme-previews.php
+++ b/wp-includes/theme-previews.php
@@ -70,7 +70,7 @@ function wp_block_theme_activate_nonce() {
 	$nonce_handle = 'switch-theme_' . wp_get_theme_preview_path();
 	?>
 	<script type="text/javascript">
-		window.WP_BLOCK_THEME_ACTIVATE_NONCE = '<?php echo wp_create_nonce( $nonce_handle ); ?>';
+		window.WP_BLOCK_THEME_ACTIVATE_NONCE = <?php echo wp_json_encode( wp_create_nonce( $nonce_handle ) ); ?>;
 	</script>
 	<?php
 }
diff --git a/wp-includes/version.php b/wp-includes/version.php
index a014de88df..be14a4e9b0 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.3-beta4-56217';
+$wp_version = '6.3-beta4-56218';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.