diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index b2eee1c8fa..2f828a4ef5 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -3939,6 +3939,22 @@ final class WP_Customize_Manager {
 	 * @since 4.1.0
 	 */
 	public function render_control_templates() {
+		if ( $this->branching() ) {
+			$l10n = array(
+				/* translators: %s: User who is customizing the changeset in customizer. */
+				'locked' => __( '%s is already customizing this changeset. Please wait until they are done to try customizing. Your latest changes have been autosaved.' ),
+				/* translators: %s: User who is customizing the changeset in customizer. */
+				'locked_allow_override' => __( '%s is already customizing this changeset. Do you want to take over?' ),
+			);
+		} else {
+			$l10n = array(
+				/* translators: %s: User who is customizing the changeset in customizer. */
+				'locked' => __( '%s is already customizing this site. Please wait until they are done to try customizing. Your latest changes have been autosaved.' ),
+				/* translators: %s: User who is customizing the changeset in customizer. */
+				'locked_allow_override' => __( '%s is already customizing this site. Do you want to take over?' ),
+			);
+		}
+
 		foreach ( $this->registered_control_types as $control_type ) {
 			$control = new $control_type( $this, 'temp', array(
 				'settings' => array(),
@@ -4101,13 +4117,11 @@ final class WP_Customize_Manager {
 							{{{ data.message }}}
 						<# } else if ( data.allowOverride ) { #>
 							<?php
-							/* translators: %s: User who is customizing the changeset in customizer. */
-							printf( __( '%s is already customizing this site. Do you want to take over?' ), '{{ data.lockUser.name }}' );
+							echo esc_html( sprintf( $l10n['locked_allow_override'], '{{ data.lockUser.name }}' ) );
 							?>
 						<# } else { #>
 							<?php
-							/* translators: %s: User who is customizing the changeset in customizer. */
-							printf( __( '%s is already customizing this site. Please wait until they are done to try customizing. Your latest changes have been autosaved.' ), '{{ data.lockUser.name }}' );
+							echo esc_html( sprintf( $l10n['locked'], '{{ data.lockUser.name }}' ) );
 							?>
 						<# } #>
 					</p>
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 0ca3b66f48..825694315b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9.3-alpha-42537';
+$wp_version = '4.9.3-alpha-42539';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.