diff --git a/src/sunstone/sunstone-server.rb b/src/sunstone/sunstone-server.rb
index 799837e50a..6e12fff0c4 100755
--- a/src/sunstone/sunstone-server.rb
+++ b/src/sunstone/sunstone-server.rb
@@ -417,7 +417,7 @@ post '/upload'do
 
     if (rackinput.class == Tempfile)
         tmpfile = rackinput
-    elsif (rackinput.class == StringIO || rackinput.class == PhusionPassenger::Utils::RewindableInput)
+    elsif rackinput.respond_to?('read')
         tmpfile = Tempfile.open('sunstone-upload')
         tmpfile.write rackinput.read
         tmpfile.flush