Index: src/wp-includes/admin-bar.php
===================================================================
--- src/wp-includes/admin-bar.php	(revision 31448)
+++ src/wp-includes/admin-bar.php	(working copy)
@@ -794,6 +794,7 @@
 		return;
 
 	$form  = '<form action="' . esc_url( home_url( '/' ) ) . '" method="get" id="adminbarsearch">';
+	$form .= '<label for="adminbar-search" class="screen-reader-text">' . __( 'Search' ) . '</label>';
 	$form .= '<input class="adminbar-input" name="s" id="adminbar-search" type="text" value="" maxlength="150" />';
 	$form .= '<input type="submit" class="adminbar-button" value="' . __('Search') . '"/>';
 	$form .= '</form>';