diff --git a/includes/class-wc-ajax.php b/includes/class-wc-ajax.php
index 21e9b7cc247..10b4d4cc55c 100644
--- a/includes/class-wc-ajax.php
+++ b/includes/class-wc-ajax.php
@@ -925,6 +925,7 @@ class WC_AJAX {
 				$validation_error = apply_filters( 'woocommerce_ajax_add_order_item_validation', $validation_error, $product, $order, $qty );
 
 				if ( $validation_error->get_error_code() ) {
+					/* translators: %s: error message */
 					throw new Exception( sprintf( __( 'Error: %s', 'woocommerce' ), $validation_error->get_error_message() ) );
 				}
 				$item_id                 = $order->add_product( $product, $qty );