diff --git a/wp-content/themes/twentythirteen/functions.php b/wp-content/themes/twentythirteen/functions.php
index a2a467a13b..9b191b98b6 100644
--- a/wp-content/themes/twentythirteen/functions.php
+++ b/wp-content/themes/twentythirteen/functions.php
@@ -596,4 +596,5 @@ require( get_template_directory() . '/inc/custom-header.php' );
 /**
  * Adds back compat handling for WP versions pre-3.6.
  */
-require( get_template_directory() . '/inc/back-compat.php' );
+if ( version_compare( $GLOBALS['wp_version'], '3.6-alpha', '<' ) )
+	require( get_template_directory() . '/inc/back-compat.php' );
diff --git a/wp-content/themes/twentythirteen/inc/back-compat.php b/wp-content/themes/twentythirteen/inc/back-compat.php
index 4a324b088e..4cc691109a 100644
--- a/wp-content/themes/twentythirteen/inc/back-compat.php
+++ b/wp-content/themes/twentythirteen/inc/back-compat.php
@@ -1,12 +1,26 @@
 <?php
+/**
+ * Prevents Twenty Thirteen from running on WordPress versions prior to 3.6.
+ *
+ * Twenty Thirteen is not meant to be backwards compatible, since it relies on
+ * a lot of new functions and markup changes that were introduced in 3.6.
+ *
+ * @package WordPress
+ * @subpackage Twenty_Thirteen
+ * @since Twenty Thirteen 1.0
+ */
+
 /**
  * Prevent switching to Twenty Thirteen on old versions of WordPress. Switches
  * to the previously activated theme or the default theme.
+ *
+ * @since Twenty Thirteen 1.0
+ *
+ * @param string $theme_name
+ * @param WP_Theme $theme
+ * @return void
  */
 function twentythirteen_switch_theme( $theme_name, $theme ) {
-	if ( version_compare( $GLOBALS['wp_version'], '3.6-alpha', '>=' ) )
-		return;
-
 	if ( 'twentythirteen' != $theme->template )
 		switch_theme( $theme->template, $theme->stylesheet );
 	elseif ( 'twentythirteen' != WP_DEFAULT_THEME )
@@ -17,7 +31,27 @@ function twentythirteen_switch_theme( $theme_name, $theme ) {
 }
 add_action( 'after_switch_theme', 'twentythirteen_switch_theme', 10, 2 );
 
+/**
+ * Prints an update nag after an unsuccessful attempt to switch to
+ * Twenty Thirteen on WordPress versions prior to 3.6.
+ *
+ * @since Twenty Thirteen 1.0
+ *
+ * @return void
+ */
 function twentythirteen_upgrade_notice() {
-	$message = sprintf( __( 'Twenty Thirteen requires at least WordPress version 3.6. You are running version %s. Please upgrade and try again.' ), $GLOBALS['wp_version'] );
+	$message = sprintf( __( 'Twenty Thirteen requires at least WordPress version 3.6. You are running version %s. Please upgrade and try again.', 'twentythirteen' ), $GLOBALS['wp_version'] );
 	printf( '<div class="error"><p>%s</p></div>', $message );
-}
\ No newline at end of file
+}
+
+/**
+ * Prevents the Customizer from being loaded on WordPress versions prior to 3.6.
+ *
+ * @since Twenty Thirteen 1.0
+ *
+ * @return void
+ */
+function twentythirteen_customize() {
+	wp_die( sprintf( __( 'Twenty Thirteen requires at least WordPress version 3.6. You are running version %s. Please upgrade and try again.', 'twentythirteen' ), $GLOBALS['wp_version'] ) . sprintf( ' <a href="javascript:history.go(-1);">%s</a>', __( 'Go back.', 'twentythirteen' ) ) );
+}
+add_action( 'load-customize.php', 'twentythirteen_customize' );