diff --git a/wp-includes/class-wp-customize-setting.php b/wp-includes/class-wp-customize-setting.php
index c2b0f74e52..b39a317221 100644
--- a/wp-includes/class-wp-customize-setting.php
+++ b/wp-includes/class-wp-customize-setting.php
@@ -161,6 +161,7 @@ class WP_Customize_Setting {
 	 * @return mixed Null if an input isn't valid, otherwise the sanitized value.
 	 */
 	public function sanitize( $value ) {
+		$value = stripslashes_deep( $value );
 		return apply_filters( "customize_sanitize_{$this->id}", $value );
 	}