diff -r 0dc698c91ca0 -r c91418480cb0 mercurial/simplemerge.py
--- a/mercurial/simplemerge.py	Fri Jan 14 10:25:45 2022 -0800
+++ b/mercurial/simplemerge.py	Tue Dec 14 13:12:56 2021 -0800
@@ -506,7 +506,7 @@
             extrakwargs = {
                 'minimize': True,
             }
-            if name_base is not None:
+            if mode == b'merge3':
                 extrakwargs['base_marker'] = b'|||||||'
                 extrakwargs['name_base'] = name_base
                 extrakwargs['minimize'] = False