diff --git a/src/main/scala/gitbucket/core/util/StringUtil.scala b/src/main/scala/gitbucket/core/util/StringUtil.scala
index 724ab98..42cb2b5 100644
--- a/src/main/scala/gitbucket/core/util/StringUtil.scala
+++ b/src/main/scala/gitbucket/core/util/StringUtil.scala
@@ -98,8 +98,8 @@
     detector.handleData(content, 0, content.length)
     detector.dataEnd()
     detector.getDetectedCharset match {
-      case null => "UTF-8"
-      case e    => e
+      case null | "US-ASCII" => "UTF-8"
+      case e                 => e
     }
   }