diff --git a/header.php b/header.php
index 5f0d5e5fd1..ee7a393a77 100644
--- a/header.php
+++ b/header.php
@@ -29,7 +29,7 @@
 		</div><!-- .site-branding -->
 
 		<nav id="site-navigation" class="main-navigation" role="navigation">
-			<button class="menu-toggle"><?php _e( 'Primary Menu', '_s' ); ?></button>
+			<button class="menu-toggle" aria-controls="menu" aria-expanded="false"><?php _e( 'Primary Menu', '_s' ); ?></button>
 			<?php wp_nav_menu( array( 'theme_location' => 'primary' ) ); ?>
 		</nav><!-- #site-navigation -->
 	</header><!-- #masthead -->
diff --git a/js/navigation.js b/js/navigation.js
index 706e4d85b7..13a4e448f3 100644
--- a/js/navigation.js
+++ b/js/navigation.js
@@ -7,12 +7,14 @@
 	var container, button, menu;
 
 	container = document.getElementById( 'site-navigation' );
-	if ( ! container )
+	if ( ! container ) {
 		return;
+	}
 
 	button = container.getElementsByTagName( 'button' )[0];
-	if ( 'undefined' === typeof button )
+	if ( 'undefined' === typeof button ) {
 		return;
+	}
 
 	menu = container.getElementsByTagName( 'ul' )[0];
 
@@ -22,13 +24,21 @@
 		return;
 	}
 
-	if ( -1 === menu.className.indexOf( 'nav-menu' ) )
+	menu.setAttribute( 'aria-expanded', 'false' );
+
+	if ( -1 === menu.className.indexOf( 'nav-menu' ) ) {
 		menu.className += ' nav-menu';
+	}
 
 	button.onclick = function() {
-		if ( -1 !== container.className.indexOf( 'toggled' ) )
+		if ( -1 !== container.className.indexOf( 'toggled' ) ) {
 			container.className = container.className.replace( ' toggled', '' );
-		else
+			button.setAttribute( 'aria-expanded', 'false' );
+			menu.setAttribute( 'aria-expanded', 'false' );
+		} else {
 			container.className += ' toggled';
+			button.setAttribute( 'aria-expanded', 'true' );
+			menu.setAttribute( 'aria-expanded', 'true' );
+		}
 	};
 } )();