diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -68,6 +68,8 @@
 update.check = noconflict
 # Show conflicts information in `hg status`
 status.verbose = True
+# Make `hg resolve` with no action (like `-m`) fail instead of re-merging.
+resolve.explicit-re-merge = True
 
 [diff]
 git = 1