diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -4361,7 +4361,7 @@
             msg = _("not updating: %s") % stringutil.forcebytestr(inst)
             hint = inst.hint
             raise error.UpdateAbort(msg, hint=hint)
-    if modheads > 1:
+    if modheads is not None and modheads > 1:
         currentbranchheads = len(repo.branchheads())
         if currentbranchheads == modheads:
             ui.status(_("(run 'hg heads' to see heads, 'hg merge' to merge)\n"))