diff --git a/wp-includes/class-wp-customize.php b/wp-includes/class-wp-customize.php
index 33e0fef11..21ce6031d 100644
--- a/wp-includes/class-wp-customize.php
+++ b/wp-includes/class-wp-customize.php
@@ -10,6 +10,9 @@
 final class WP_Customize {
 	protected $template;
 	protected $stylesheet;
+	protected $original_template;
+	protected $original_stylesheet;
+
 	protected $previewing = false;
 
 	protected $settings = array();
@@ -81,6 +84,9 @@ final class WP_Customize {
 
 		show_admin_bar( false );
 
+		$this->original_template   = get_template();
+		$this->original_stylesheet = get_stylesheet();
+
 		add_filter( 'template', array( $this, 'get_template' ) );
 		add_filter( 'stylesheet', array( $this, 'get_stylesheet' ) );
 		add_filter( 'pre_option_current_theme', array( $this, 'current_theme' ) );
diff --git a/wp-includes/customize-controls.php b/wp-includes/customize-controls.php
index d77a3a97e..11661037e 100644
--- a/wp-includes/customize-controls.php
+++ b/wp-includes/customize-controls.php
@@ -81,7 +81,8 @@ do_action( 'customize_controls_print_scripts' );
 
 		<div id="customize-footer-actions" class="customize-section wp-full-overlay-footer">
 			<?php
-			submit_button( __( 'Save' ), 'primary', 'save', false );
+			$save_text = $this->get_stylesheet() == $this->original_stylesheet ? __('Save') : __('Save and Activate');
+			submit_button( $save_text, 'primary', 'save', false );
 			?>
 			<a href="#" class="collapse-sidebar button-secondary" title="<?php esc_attr_e('Collapse Sidebar'); ?>">
 				<span class="collapse-sidebar-label"><?php _e('Collapse'); ?></span>