diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 688b3a1..cd6e119 100644
*** a/src/backend/optimizer/prep/prepjointree.c
--- b/src/backend/optimizer/prep/prepjointree.c
*************** replace_vars_in_jointree(Node *jtnode,
*** 2044,2049 ****
--- 2044,2061 ----
  		}
  		replace_vars_in_jointree(j->larg, context, lowest_nulling_outer_join);
  		replace_vars_in_jointree(j->rarg, context, lowest_nulling_outer_join);
+ 
+ 		/*
+ 		 * Use PHVs within the join quals of a full join, even when it's the
+ 		 * lowest nulling outer join.  Otherwise, we cannot identify which
+ 		 * side of the join a pulled-up var-free expression came from, which
+ 		 * can lead to failure to make a plan at all because none of the quals
+ 		 * appear to be mergeable or hashable conditions.  For this purpose we
+ 		 * don't care about the state of wrap_non_vars, so leave it alone.
+ 		 */
+ 		if (j->jointype == JOIN_FULL)
+ 			context->need_phvs = true;
+ 
  		j->quals = pullup_replace_vars(j->quals, context);
  
  		/*