diff -r 7c20d501709b -r c1fb2cab6260 mercurial/hg.py
--- a/mercurial/hg.py	Thu Sep 24 15:47:23 2015 -0700
+++ b/mercurial/hg.py	Thu Sep 24 15:52:11 2015 -0700
@@ -582,10 +582,11 @@
                     try:
                         uprev = destrepo.lookup(checkout)
                     except error.RepoLookupError:
-                        try:
-                            uprev = destrepo.lookup(update)
-                        except error.RepoLookupError:
-                            pass
+                        if update is not True:
+                            try:
+                                uprev = destrepo.lookup(update)
+                            except error.RepoLookupError:
+                                pass
                 if uprev is None:
                     try:
                         uprev = destrepo._bookmarks['@']