diff --git a/changelog/fix-bookings-id-undefined-variable b/changelog/fix-bookings-id-undefined-variable
new file mode 100644
index 00000000000..04066ac1349
--- /dev/null
+++ b/changelog/fix-bookings-id-undefined-variable
@@ -0,0 +1,5 @@
+Significance: patch
+Type: fix
+Comment: Small defensive check for booking_id variable.
+
+
diff --git a/includes/express-checkout/class-wc-payments-express-checkout-button-helper.php b/includes/express-checkout/class-wc-payments-express-checkout-button-helper.php
index 4c42635d102..c5194b5a888 100644
--- a/includes/express-checkout/class-wc-payments-express-checkout-button-helper.php
+++ b/includes/express-checkout/class-wc-payments-express-checkout-button-helper.php
@@ -109,7 +109,7 @@ public function ajax_add_to_cart() {
 		$data          += $this->build_display_items();
 		$data['result'] = 'success';
 
-		if ( $booking_id ) {
+		if ( ! empty( $booking_id ) ) {
 			$data['bookingId'] = $booking_id;
 		}