diff --git a/src/Renderers/SpanNodeRenderer.php b/src/Renderers/SpanNodeRenderer.php
index 927c3fa..e1e7775 100644
--- a/src/Renderers/SpanNodeRenderer.php
+++ b/src/Renderers/SpanNodeRenderer.php
@@ -32,7 +32,7 @@ public function __construct(
         SpanNode $span,
         BaseSpanNodeRenderer $decoratedSpanNodeRenderer,
         ?UrlChecker $urlChecker = null,
-        string $symfonyVersion = null
+        ?string $symfonyVersion = null
     )
     {
         parent::__construct($environment, $span);
diff --git a/src/SymfonyHTMLFormat.php b/src/SymfonyHTMLFormat.php
index 9c17ca9..16ea957 100644
--- a/src/SymfonyHTMLFormat.php
+++ b/src/SymfonyHTMLFormat.php
@@ -29,7 +29,7 @@ final class SymfonyHTMLFormat implements Format
     private $urlChecker;
     private $symfonyVersion;
 
-    public function __construct(TemplateRenderer $templateRenderer, Format $HTMLFormat, ?UrlChecker $urlChecker = null, string $symfonyVersion = null)
+    public function __construct(TemplateRenderer $templateRenderer, Format $HTMLFormat, ?UrlChecker $urlChecker = null, ?string $symfonyVersion = null)
     {
         $this->templateRenderer = $templateRenderer;
         $this->htmlFormat = $HTMLFormat;