diff --git a/modules/tax/src/Plugin/Commerce/TaxType/Custom.php b/modules/tax/src/Plugin/Commerce/TaxType/Custom.php
index 2a4565f..c1fd738 100644
--- a/modules/tax/src/Plugin/Commerce/TaxType/Custom.php
+++ b/modules/tax/src/Plugin/Commerce/TaxType/Custom.php
@@ -382,7 +382,7 @@ class Custom extends LocalTaxTypeBase {
     // start/end dates for UX reasons, so a start date is invented here.
     foreach ($rates as &$rate) {
       $rate['percentages'][] = [
-        'number' => $rate['percentage'],
+        'number' => (string) $rate['percentage'],
         'start_date' => '2000-01-01',
       ];
       unset($rate['percentage']);