diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -240,7 +240,7 @@ def bisected(repo, subset, x):
     Changesets marked in the specified bisect state (good, bad, skip).
     """
     state = getstring(x, _("bisect requires a string")).lower()
-    if state not in ('good', 'bad', 'skip', 'unknown'):
+    if state not in ('good', 'bad', 'skip'):
         raise error.ParseError(_('invalid bisect state'))
     marked = set(repo.changelog.rev(n) for n in hbisect.load_state(repo)[state])
     return [r for r in subset if r in marked]