Index: /pyyaml/trunk/lib/yaml/emitter.py
===================================================================
--- /pyyaml/trunk/lib/yaml/emitter.py	(revision 333)
+++ /pyyaml/trunk/lib/yaml/emitter.py	(revision 345)
@@ -582,5 +582,7 @@
         handle = None
         suffix = tag
-        for prefix in self.tag_prefixes:
+        prefixes = self.tag_prefixes.keys()
+        prefixes.sort()
+        for prefix in prefixes:
             if tag.startswith(prefix)   \
                     and (prefix == u'!' or len(prefix) < len(tag)):