app-functions-fn.cart.php.diff

diff --git a/app/functions/fn.cart.php b/app/functions/fn.cart.php
index da13a21d8c..79ec8fa47e 100644
--- a/app/functions/fn.cart.php
+++ b/app/functions/fn.cart.php
@@ -794,7 +794,9 @@ function fn_update_currency($currency_data, $currency_id, $lang_code = DESCR_SL)
     fn_set_hook('update_currency_pre', $currency_data, $currency_id, $lang_code);
 
     $currency_data['currency_code'] = strtoupper($currency_data['currency_code']);
-    $currency_data['coefficient'] = !empty($currency_data['is_primary']) || !isset($currency_data['coefficient']) ? 1 : $currency_data['coefficient'];
+
+    $is_primary_currency = !empty($currency_data['is_primary']) && YesNo::toBool($currency_data['is_primary']);
+    $currency_data['coefficient'] = $is_primary_currency || !isset($currency_data['coefficient']) ? 1 : $currency_data['coefficient'];
     $currency_data['symbol'] = empty($currency_data['symbol']) ? '' : SecurityHelper::sanitizeHtml($currency_data['symbol']);
 
     if (empty($currency_data['coefficient']) || floatval($currency_data['coefficient']) <= 0) {
@@ -820,7 +822,7 @@ function fn_update_currency($currency_data, $currency_id, $lang_code = DESCR_SL)
         )));
     }
 
-    if (!empty($currency_data['is_primary']) && $currency_data['is_primary'] === YesNo::YES) {
+    if ($is_primary_currency) {
         db_query("UPDATE ?:currencies SET is_primary = 'N' WHERE is_primary = 'Y'");
     }