diff --git a/src/Document.php b/src/Document.php
index e2ca461d..716b218a 100644
--- a/src/Document.php
+++ b/src/Document.php
@@ -32,7 +32,7 @@ public function __construct(Extractor $extractor)
         if (!empty($match[1])) {
             $encoding = trim($match[1], ',');
             try {
-                $ret = mb_encoding_aliases($encoding);
+                $ret = mb_encoding_aliases($encoding ?? '');
                 if ($ret === false) {
                     $encoding = null;
                 }
@@ -46,7 +46,7 @@ public function __construct(Extractor $extractor)
                 $encoding = trim($match[1], ',');
             }
             try {
-                $ret = mb_encoding_aliases($encoding);
+                $ret = mb_encoding_aliases($encoding ?? '');
                 if ($ret === false) {
                     $encoding = null;
                 }