Index: src/wp-admin/includes/meta-boxes.php
===================================================================
--- src/wp-admin/includes/meta-boxes.php	(revision 40304)
+++ src/wp-admin/includes/meta-boxes.php	(working copy)
@@ -50,10 +50,15 @@
 <?php
 $preview_link = esc_url( get_preview_post_link( $post ) );
 if ( 'publish' == $post->post_status ) {
-	$preview_button = __( 'Preview Changes' );
+	$preview_button_text = __( 'Preview Changes' );
 } else {
-	$preview_button = __( 'Preview' );
+	$preview_button_text = __( 'Preview' );
 }
+
+$preview_button = sprintf( '%1$s<span class="screen-reader-text"> %2$s</span>',
+        esc_html( $preview_button_text ),
+        /* translators: accessibility text */
+        esc_html__( '(link opens in a new window)' ) );
 ?>
 <a class="preview button" href="<?php echo $preview_link; ?>" target="wp-preview-<?php echo (int) $post->ID; ?>" id="post-preview"><?php echo $preview_button; ?></a>
 <input type="hidden" name="wp-preview" id="wp-preview" value="" />