--- a/mercurial/merge.py	Sat Sep 07 14:35:21 2019 +0100
+++ b/mercurial/merge.py	Wed Sep 18 17:53:10 2019 +0700
@@ -2256,7 +2256,7 @@
         pother = nullid
         parents = ctx.parents()
         if keepparent and len(parents) == 2 and pctx in parents:
-            if pctx == parents[0]:
+            if pctx == parents[1]:
                 potherp1 = True
             parents.remove(pctx)
             pother = parents[0].node()