diff --git a/src/Fetch/MIME.php b/src/Fetch/MIME.php
index b63d72b..8f0c328 100644
--- a/src/Fetch/MIME.php
+++ b/src/Fetch/MIME.php
@@ -36,7 +36,9 @@ public static function decode($text, $targetCharset = 'utf-8')
 
         foreach (imap_mime_header_decode($text) as $word) {
             $ch = 'default' === $word->charset ? 'ascii' : $word->charset;
-
+            if ($ch==="ascii" && ($c=strtoupper(mb_detect_encoding($word->text)))!==strtoupper($ch)) {
+            	$ch=$c;
+            }
             $result .= iconv($ch, $targetCharset, $word->text);
         }
 
diff --git a/src/Fetch/Message.php b/src/Fetch/Message.php
index e382678..ed897c2 100755
--- a/src/Fetch/Message.php
+++ b/src/Fetch/Message.php
@@ -523,7 +523,7 @@ protected function processStructure($structure, $partIdentifier = null)
             if (!empty($parameters['charset']) && $parameters['charset'] !== self::$charset) {
                 $mb_converted = false;
                 if (function_exists('mb_convert_encoding')) {
-                    if (!in_array($parameters['charset'], mb_list_encodings())) {
+                    if (!in_array(strtolower($parameters['charset']), array_map("strtolower", mb_list_encodings()))) {
                         if ($structure->encoding === 0) {
                             $parameters['charset'] = 'US-ASCII';
                         } else {
@@ -531,11 +531,11 @@ protected function processStructure($structure, $partIdentifier = null)
                         }
                     }
 
-                    $messageBody = @mb_convert_encoding($messageBody, self::$charset, $parameters['charset']);
+                    $messageBody = @mb_convert_encoding($messageBody, self::$charset, strtoupper($parameters['charset']));
                     $mb_converted = true;
                 }
                 if (!$mb_converted) {
-                    $messageBodyConv = @iconv($parameters['charset'], self::$charset . self::$charsetFlag, $messageBody);
+                    $messageBodyConv = @iconv(strtoupper($parameters['charset']), self::$charset . self::$charsetFlag, $messageBody);
 
                     if ($messageBodyConv !== false) {
                         $messageBody = $messageBodyConv;