diff --git a/src/wp-admin/js/customize-controls.js b/src/wp-admin/js/customize-controls.js
index 951fb4cfd0..831a46e240 100644
--- a/src/wp-admin/js/customize-controls.js
+++ b/src/wp-admin/js/customize-controls.js
@@ -2023,7 +2023,7 @@
 				response = response.slice( 0, index ) + response.slice( index + signature.length );
 
 				// Create the iframe and inject the html content.
-				self.iframe = $('<iframe />').appendTo( self.container );
+				self.iframe = $( '<iframe />', { 'title': api.l10n.previewIframeTitle } ).appendTo( self.container );
 
 				// Bind load event after the iframe has been added to the page;
 				// otherwise it will fire when injected into the DOM.
@@ -2055,8 +2055,9 @@
 				deferred.rejectWith( self, [ 'logged out' ] );
 			};
 
-			if ( this.triedLogin )
+			if ( this.triedLogin ) {
 				return reject();
+			}
 
 			// Check if we have an admin cookie.
 			$.get( api.settings.url.ajax, {
@@ -2064,10 +2065,11 @@
 			}).fail( reject ).done( function( response ) {
 				var iframe;
 
-				if ( '1' !== response )
+				if ( '1' !== response ) {
 					reject();
+				}
 
-				iframe = $('<iframe src="' + self.previewUrl() + '" />').hide();
+				iframe = $( '<iframe />', { 'src': self.previewUrl(), 'title': api.l10n.previewIframeTitle } ).hide();
 				iframe.appendTo( self.container );
 				iframe.load( function() {
 					self.triedLogin = true;
@@ -2327,7 +2329,7 @@
 				url:     api.settings.url.login
 			});
 
-			iframe = $('<iframe src="' + api.settings.url.login + '" />').appendTo( this.container );
+			iframe = $( '<iframe />', { 'src': api.settings.url.login, 'title': api.l10n.loginIframeTitle } ).appendTo( this.container );
 
 			messenger.targetWindow( iframe[0].contentWindow );
 
diff --git a/src/wp-admin/theme-install.php b/src/wp-admin/theme-install.php
index 0443ba854e..73e343a9a9 100644
--- a/src/wp-admin/theme-install.php
+++ b/src/wp-admin/theme-install.php
@@ -260,7 +260,7 @@ if ( $tab ) {
 		</div>
 	</div>
 	<div class="wp-full-overlay-main">
-		<iframe src="{{ data.preview_url }}" />
+		<iframe src="{{ data.preview_url }}" title="<?php esc_attr_e( 'Preview' ); ?>" />
 	</div>
 </script>
 
diff --git a/src/wp-includes/js/customize-loader.js b/src/wp-includes/js/customize-loader.js
index 07f21966a9..02ddc67bab 100644
--- a/src/wp-includes/js/customize-loader.js
+++ b/src/wp-includes/js/customize-loader.js
@@ -114,7 +114,7 @@ window.wp = window.wp || {};
 			// Dirty state of Customizer in iframe
 			this.saved = new api.Value( true );
 
-			this.iframe = $( '<iframe />', { src: src }).appendTo( this.element );
+			this.iframe = $( '<iframe />', { 'src': src, 'title': Loader.settings.l10n.mainIframeTitle } ).appendTo( this.element );
 			this.iframe.one( 'load', this.loaded );
 
 			// Create a postMessage connection with the iframe.
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 2c5fa809c3..97fb68183f 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -389,13 +389,15 @@ function wp_default_scripts( &$scripts ) {
 	$scripts->add( 'customize-views',    "/wp-includes/js/customize-views.js",  array( 'jquery', 'underscore', 'imgareaselect', 'customize-models' ), false, 1 );
 	$scripts->add( 'customize-controls', "/wp-admin/js/customize-controls$suffix.js", array( 'customize-base' ), false, 1 );
 	did_action( 'init' ) && $scripts->localize( 'customize-controls', '_wpCustomizeControlsL10n', array(
-		'activate'  => __( 'Save &amp; Activate' ),
-		'save'      => __( 'Save &amp; Publish' ),
-		'saveAlert' => __( 'The changes you made will be lost if you navigate away from this page.' ),
-		'saved'     => __( 'Saved' ),
-		'cancel'    => __( 'Cancel' ),
-		'close'     => __( 'Close' ),
-		'cheatin'   => __( 'Cheatin&#8217; uh?' ),
+		'activate'           => __( 'Save &amp; Activate' ),
+		'save'               => __( 'Save &amp; Publish' ),
+		'saveAlert'          => __( 'The changes you made will be lost if you navigate away from this page.' ),
+		'saved'              => __( 'Saved' ),
+		'cancel'             => __( 'Cancel' ),
+		'close'              => __( 'Close' ),
+		'cheatin'            => __( 'Cheatin&#8217; uh?' ),
+		'previewIframeTitle' => __( 'Site Preview' ),
+		'loginIframeTitle'   => __( 'Session expired' ),
 
 		// Used for overriding the file types allowed in plupload.
 		'allowedFiles' => __( 'Allowed Files' ),
diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index d2eb765edf..ac52fba757 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -1963,7 +1963,8 @@ function _wp_customize_loader_settings() {
 		'isCrossDomain' => $cross_domain,
 		'browser'       => $browser,
 		'l10n'          => array(
-			'saveAlert' => __( 'The changes you made will be lost if you navigate away from this page.' ),
+			'saveAlert'       => __( 'The changes you made will be lost if you navigate away from this page.' ),
+			'mainIframeTitle' => __( 'Customizer' ),
 		),
 	);