diff --git a/includes/Core/Conversion_Tracking/Conversion_Event_Providers/WooCommerce.php b/includes/Core/Conversion_Tracking/Conversion_Event_Providers/WooCommerce.php
index 518ca868941..22fd237a8d5 100644
--- a/includes/Core/Conversion_Tracking/Conversion_Event_Providers/WooCommerce.php
+++ b/includes/Core/Conversion_Tracking/Conversion_Event_Providers/WooCommerce.php
@@ -94,7 +94,7 @@ function ( $order_id ) use ( $input ) {
 				$order_key = $input->filter( INPUT_GET, 'key' );
 
 				// Don't output the script tag if the order key is invalid.
-				if ( ! $order->key_is_valid( $order_key ) ) {
+				if ( ! $order->key_is_valid( (string) $order_key ) ) {
 					return;
 				}