--- a/mercurial/archival.py	Tue Feb 05 14:02:03 2008 +0100
+++ b/mercurial/archival.py	Tue Feb 05 15:54:42 2008 +0100
@@ -208,6 +208,8 @@
         archiver.addfile(name, mode, islink, data)
 
     ctx = repo.changectx(node)
+    if kind not in archivers:
+        raise util.Abort(_("unknown archive type '%s'" % kind))
     archiver = archivers[kind](dest, prefix, mtime or ctx.date()[0])
     m = ctx.manifest()
     items = m.items()