diff --git a/imp/lib/Contents/View.php b/imp/lib/Contents/View.php
index 61679971327..ffb045d445c 100644
--- a/imp/lib/Contents/View.php
+++ b/imp/lib/Contents/View.php
@@ -189,7 +189,7 @@ public function viewSource()
                 'stream' => true
             )),
             'name' => _("Message Source"),
-            'type' => 'text/plain'
+            'type' => 'text/plain; charset=UTF-8'
         );
     }