Index: pyyaml/trunk/lib/yaml/emitter.py
===================================================================
--- pyyaml/trunk/lib/yaml/emitter.py	(revision 328)
+++ pyyaml/trunk/lib/yaml/emitter.py	(revision 333)
@@ -155,5 +155,5 @@
     def expect_stream_start(self):
         if isinstance(self.event, StreamStartEvent):
-            if self.event.encoding:
+            if self.event.encoding and not getattr(self.stream, 'encoding', None):
                 self.encoding = self.event.encoding
             self.write_stream_start()