--- money.module~	2007-09-10 21:25:43.000000000 +0100
+++ money.module	2007-09-10 21:34:21.000000000 +0100
@@ -119,7 +119,7 @@ function money_field($op, &$node, $field
             form_set_error($field['field_name'] .']['. $delta .'][currency', t('The currency %currency is not allowed.', array('%currency' => t($item['currency']))));
           }
           // Validate the amount.
-          if (!is_numeric($item['amount'])) {
+          if ($item['amount'] != '' && !is_numeric($item['amount'])) {
             form_set_error($field['field_name'] .']['. $delta .'][amount', t('You entered an invalid amount.'));
           }
         }