--- a/mercurial/merge.py
+++ b/mercurial/merge.py
@@ -384,9 +384,13 @@ def update(repo, node, branchmerge, forc
if branchmerge:
raise util.Abort(_("there is nothing to merge, just use "
"'hg update' or look at 'hg heads'"))
- elif not (overwrite or branchmerge):
- raise util.Abort(_("update spans branches, use 'hg merge' "
- "or 'hg update -C' to lose changes"))
+ elif not branchmerge:
+ if not overwrite:
+ if wc.files():
+ raise util.Abort(_("outstanding uncommited changes, use "
+ "'hg update -C' to lose changes"))
+ else:
+ overwrite = True
if branchmerge and not forcemerge:
if wc.modified() or wc.added() or wc.removed():
raise util.Abort(_("outstanding uncommitted changes"))