diff -r 0680b8a1992a -r c482e2fe444c hgext/phabricator.py
--- a/hgext/phabricator.py	Tue Mar 03 17:37:09 2020 -0500
+++ b/hgext/phabricator.py	Sun Apr 12 13:11:42 2020 -0400
@@ -1304,6 +1304,9 @@
 
     ctxs = [repo[rev] for rev in revs]
 
+    if any(c for c in ctxs if c.obsolete()):
+        raise error.Abort(_(b"obsolete commits cannot be posted for review"))
+
     fold = opts.get(b'fold')
     if fold:
         if len(revs) == 1: