diff --git a/lib/sup/maildir.rb b/lib/sup/maildir.rb
index 0852576..899625d 100644
--- a/lib/sup/maildir.rb
+++ b/lib/sup/maildir.rb
@@ -34,6 +34,12 @@ class Maildir < Source
     #is a worthwhile effort
     @mtimes = { 'cur' => Time.at(0), 'new' => Time.at(0) }.merge(mtimes || {})
     @dir_ids = { 'cur' => [], 'new' => [] }
+    if RUBY_VERSION < "1.9"
+      @bin = ''
+    else
+      @bin = ':BINARY'
+    end
+
   end
 
   def file_path; @dir end
@@ -59,7 +65,7 @@ class Maildir < Source
         File.stat(tmp_path)
       rescue Errno::ENOENT #this is what we want.
         begin
-          File.open(tmp_path, 'wb:BINARY') do |f|
+          File.open(tmp_path, "wb#{@bin}") do |f|
             yield f #provide a writable interface for the caller
             f.fsync
           end
@@ -207,7 +213,7 @@ private
   def with_file_for id
     fn = @ids_to_fns[id] or raise OutOfSyncSourceError, "No such id: #{id.inspect}."
     begin
-      File.open(fn, 'rb:BINARY') { |f| yield f }
+      File.open(fn, "rb#{@bin}") { |f| yield f }
     rescue SystemCallError, IOError => e
       raise FatalSourceError, "Problem reading file for id #{id.inspect}: #{fn.inspect}: #{e.message}."
     end