diff --git a/composer.json b/composer.json
index 43ca4a1..c71d238 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,9 @@
     }
   ],
   "require": {
-    "php": ">=5.3.0",
+    "php": ">=5.3.0"
+  },
+  "suggest": {
     "ext-imap": "*"
   },
   "require-dev": {
diff --git a/src/Fetch/Message.php b/src/Fetch/Message.php
index e382678..647130d 100755
--- a/src/Fetch/Message.php
+++ b/src/Fetch/Message.php
@@ -524,10 +524,8 @@ protected function processStructure($structure, $partIdentifier = null)
                 $mb_converted = false;
                 if (function_exists('mb_convert_encoding')) {
                     if (!in_array($parameters['charset'], mb_list_encodings())) {
-                        if ($structure->encoding === 0) {
+                        if (empty($structure->encoding)) {
                             $parameters['charset'] = 'US-ASCII';
-                        } else {
-                            $parameters['charset'] = 'UTF-8';
                         }
                     }