diff -r f330d6117a5b -r 61719b9658b1 mercurial/commands.py
--- a/mercurial/commands.py	Sat May 30 12:36:00 2020 -0400
+++ b/mercurial/commands.py	Wed Jun 03 19:20:18 2020 +0900
@@ -2971,9 +2971,6 @@
 
     revs = list(revs)
     revs.extend(opts.get(b'rev'))
-    basectx = None
-    if opts.get(b'base'):
-        basectx = scmutil.revsingle(repo, opts[b'base'], None)
     # a dict of data to be stored in state file
     statedata = {}
     # list of new nodes created by ongoing graft
@@ -3063,6 +3060,8 @@
                 opts[b'log'] = True
             if statedata.get(b'no_commit'):
                 opts[b'no_commit'] = statedata.get(b'no_commit')
+            if statedata.get(b'base'):
+                opts[b'base'] = statedata.get(b'base')
             nodes = statedata[b'nodes']
             revs = [repo[node].rev() for node in nodes]
         else:
@@ -3075,6 +3074,9 @@
         revs = scmutil.revrange(repo, revs)
 
     skipped = set()
+    basectx = None
+    if opts.get(b'base'):
+        basectx = scmutil.revsingle(repo, opts[b'base'], None)
     if basectx is None:
         # check for merges
         for rev in repo.revs(b'%ld and merge()', revs):
@@ -3167,6 +3169,8 @@
 
     if opts.get(b'no_commit'):
         statedata[b'no_commit'] = True
+    if opts.get(b'base'):
+        statedata[b'base'] = opts[b'base']
     for pos, ctx in enumerate(repo.set(b"%ld", revs)):
         desc = b'%d:%s "%s"' % (
             ctx.rev(),