Index: wp-includes/class-wp-editor.php
===================================================================
--- wp-includes/class-wp-editor.php	(revision 26747)
+++ wp-includes/class-wp-editor.php	(working copy)
@@ -729,7 +729,7 @@
 
 			<div<?php if ( $args['both'] ) { ?> class="wp-fullscreen-both"<?php } ?>>
 			<a title="<?php echo $args['title']; ?>" onclick="<?php echo $args['onclick']; ?>return false;" class="mceButton mceButtonEnabled mce_<?php echo $button; ?>" href="#" id="wp_fs_<?php echo $button; ?>" role="button" aria-pressed="false">
-			<span class="mceIcon mce_<?php echo $button; ?>"></span>
+			<span class="mceIcon mce_<?php echo $button; ?>"><span class="screen-reader-text"><?php echo $args['title']; ?></span></span>
 			</a>
 			</div>
 	<?php