diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -7472,6 +7472,9 @@ def tag(ui, repo, name1, *names, **opts)
                 )
         node = logcmdutil.revsingle(repo, rev_).node()
 
+        if node is None:
+            raise error.InputError(_(b"cannot tag working directory"))
+
         if not message:
             # we don't translate commit messages
             message = b'Added tag %s for changeset %s' % (
diff --git a/tests/test-tag.t b/tests/test-tag.t
--- a/tests/test-tag.t
+++ b/tests/test-tag.t
@@ -412,6 +412,10 @@ tagging on null rev
   abort: cannot tag null revision
   [10]
 
+  $ hg tag -R empty -r "wdir()" -f wdirtag
+  abort: cannot tag working directory
+  [10]
+
 issue5539: pruned tags do not appear in .hgtags
 
   $ cat >> $HGRCPATH << EOF