diff -r 96d0795bd0bd -r e9740c07158d mercurial/ui.py
--- a/mercurial/ui.py	Fri Aug 03 12:57:44 2018 -0700
+++ b/mercurial/ui.py	Fri Aug 03 12:59:01 2018 -0700
@@ -67,6 +67,9 @@
 update.check = noconflict
 # Show conflicts information in `hg status`
 status.verbose = True
+# Refuse to perform `hg resolve --mark` on files that still have conflict
+# markers
+resolve.mark-check = abort
 
 [diff]
 git = 1