diff --git a/.github/workflows/phpunit.yml b/.github/workflows/phpunit.yml
index 8be9545..96b6dc0 100644
--- a/.github/workflows/phpunit.yml
+++ b/.github/workflows/phpunit.yml
@@ -23,6 +23,7 @@ jobs:
           - "8.1"
           - "8.2"
           - "8.3"
+          - "8.4"
 
     steps:
 
diff --git a/src/FontLib/TrueType/File.php b/src/FontLib/TrueType/File.php
index ee3c84e..f4c797a 100644
--- a/src/FontLib/TrueType/File.php
+++ b/src/FontLib/TrueType/File.php
@@ -100,7 +100,7 @@ class File extends BinaryStream {
     "Ccaron", "ccaron", "dmacron"
   );
 
-  private function uniord (string $c, string $encoding = null) {
+  private function uniord (string $c, ?string $encoding = null) {
     if (function_exists("mb_ord")) {
       if (PHP_VERSION_ID < 80000 && $encoding === null) {
           // in PHP < 8 the encoding argument, if supplied, must be a valid encoding