diff --git a/app/Support/Twig/AmountFormat.php b/app/Support/Twig/AmountFormat.php
index ad712e781f..1a1a6a2abf 100644
--- a/app/Support/Twig/AmountFormat.php
+++ b/app/Support/Twig/AmountFormat.php
@@ -123,7 +123,7 @@ class AmountFormat extends Twig_Extension
         return new Twig_SimpleFunction(
             'formatAmountBySymbol',
             /** @noinspection MoreThanThreeArgumentsInspection */
-            function (string $amount, string $symbol, int $decimalPlaces = null, bool $coloured = null): string {
+            static function (string $amount, string $symbol, int $decimalPlaces = null, bool $coloured = null): string {
                 $decimalPlaces            = $decimalPlaces ?? 2;
                 $coloured                 = $coloured ?? true;
                 $currency                 = new TransactionCurrency;