Index: wp-includes/class-wp-editor.php
===================================================================
--- wp-includes/class-wp-editor.php	(revision 26905)
+++ wp-includes/class-wp-editor.php	(working copy)
@@ -897,7 +897,7 @@
 			?>
 
 			<div class="mce-widget mce-btn<?php if ( $args['both'] ) { ?> wp-fullscreen-both<?php } ?>">
-			<button type="button" role="presentation" title="<?php echo $args['title']; ?>"<?php echo $onclick; ?> id="wp_fs_<?php echo $button; ?>">
+			<button type="button" aria-label="<?php echo $args['title']; ?>" title="<?php echo $args['title']; ?>"<?php echo $onclick; ?> id="wp_fs_<?php echo $button; ?>">
 				<i class="mce-ico mce-i-<?php echo $button; ?>"></i>
 			</button>
 			</div>