diff --git a/src/StringEncoder/DTO/EncodingDTO.php b/src/StringEncoder/DTO/EncodingDTO.php
index cfa9af9..2273edb 100644
--- a/src/StringEncoder/DTO/EncodingDTO.php
+++ b/src/StringEncoder/DTO/EncodingDTO.php
@@ -32,7 +32,7 @@ private function __construct(string $encoding, ?Validator $validator = null, Opt
             $options = new Options();
         }
 
-        if (!$validator->validateEncoding($encoding, $options->isCaseSensitiveEncoding())) {
+        if (!$validator->validateEncoding(strtoupper($encoding), $options->isCaseSensitiveEncoding())) {
             throw new InvalidEncodingException('Encoding "' . $encoding . '" is not supported by this system.');
         }
         if (!$options->isCaseSensitiveEncoding()) {