diff --git a/lib/sup/message-chunks.rb b/lib/sup/message-chunks.rb
index c275f41..b0f934e 100644
--- a/lib/sup/message-chunks.rb
+++ b/lib/sup/message-chunks.rb
@@ -34,7 +34,11 @@ require 'tempfile'
 ## monkey-patch time: make temp files have the right extension
 class Tempfile
   def make_tmpname basename, n
-    sprintf '%d-%d-%s', $$, n, basename
+    if n
+      sprintf '%d-%d-%s', $$, n, basename
+    else
+      sprintf '%d-%s', $$, basename
+    end
   end
 end