diff --git a/src/ExtensionMimeTypeDetector.php b/src/ExtensionMimeTypeDetector.php
index cd34462..0caa5fe 100644
--- a/src/ExtensionMimeTypeDetector.php
+++ b/src/ExtensionMimeTypeDetector.php
@@ -13,7 +13,7 @@ class ExtensionMimeTypeDetector implements MimeTypeDetector, ExtensionLookup
      */
     private $extensions;
 
-    public function __construct(ExtensionToMimeTypeMap $extensions = null)
+    public function __construct(?ExtensionToMimeTypeMap $extensions = null)
     {
         $this->extensions = $extensions ?: new GeneratedExtensionToMimeTypeMap();
     }
diff --git a/src/FinfoMimeTypeDetector.php b/src/FinfoMimeTypeDetector.php
index 8084f92..2ccf328 100644
--- a/src/FinfoMimeTypeDetector.php
+++ b/src/FinfoMimeTypeDetector.php
@@ -41,7 +41,7 @@ class FinfoMimeTypeDetector implements MimeTypeDetector, ExtensionLookup
 
     public function __construct(
         string $magicFile = '',
-        ExtensionToMimeTypeMap $extensionMap = null,
+        ?ExtensionToMimeTypeMap $extensionMap = null,
         ?int $bufferSampleSize = null,
         array $inconclusiveMimetypes = self::INCONCLUSIVE_MIME_TYPES
     ) {