diff --git a/src/backend/optimizer/util/placeholder.c b/src/backend/optimizer/util/placeholder.c
index 3b0f0584f0..f0e8cd9965 100644
--- a/src/backend/optimizer/util/placeholder.c
+++ b/src/backend/optimizer/util/placeholder.c
@@ -400,14 +400,16 @@ add_placeholders_to_base_rels(PlannerInfo *root)
 
 /*
  * add_placeholders_to_joinrel
- *		Add any required PlaceHolderVars to a join rel's targetlist;
- *		and if they contain lateral references, add those references to the
- *		joinrel's direct_lateral_relids.
+ *		Add any newly-computable PlaceHolderVars to a join rel's targetlist;
+ *		and if computable PHVs contain lateral references, add those
+ *		references to the joinrel's direct_lateral_relids.
  *
  * A join rel should emit a PlaceHolderVar if (a) the PHV can be computed
  * at or below this join level and (b) the PHV is needed above this level.
- * However, condition (a) is sufficient to add to direct_lateral_relids,
- * as explained below.
+ * Our caller build_join_rel() has already added any PHVs that were computed
+ * in either join input rel, so we need add only newly-computable ones to
+ * the targetlist.  However, direct_lateral_relids must be updated for every
+ * PHV computable at or below this join, as explained below.
  */
 void
 add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
@@ -426,13 +428,10 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 			/* Is it still needed above this joinrel? */
 			if (bms_nonempty_difference(phinfo->ph_needed, relids))
 			{
-				/* Yup, add it to the output */
-				joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
-													phinfo->ph_var);
-				joinrel->reltarget->width += phinfo->ph_width;
-
 				/*
-				 * Charge the cost of evaluating the contained expression if
+				 * Yes, but only add to tlist if it wasn't computed in either
+				 * input; otherwise it should be there already.  Also, we
+				 * charge the cost of evaluating the contained expression if
 				 * the PHV can be computed here but not in either input.  This
 				 * is a bit bogus because we make the decision based on the
 				 * first pair of possible input relations considered for the
@@ -445,12 +444,15 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 				if (!bms_is_subset(phinfo->ph_eval_at, outer_rel->relids) &&
 					!bms_is_subset(phinfo->ph_eval_at, inner_rel->relids))
 				{
+					PlaceHolderVar *phv = phinfo->ph_var;
 					QualCost	cost;
 
-					cost_qual_eval_node(&cost, (Node *) phinfo->ph_var->phexpr,
-										root);
+					joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
+														phv);
+					cost_qual_eval_node(&cost, (Node *) phv->phexpr, root);
 					joinrel->reltarget->cost.startup += cost.startup;
 					joinrel->reltarget->cost.per_tuple += cost.per_tuple;
+					joinrel->reltarget->width += phinfo->ph_width;
 				}
 			}
 
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 520409f4ba..442c12acef 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -688,6 +688,8 @@ build_join_rel(PlannerInfo *root,
 	 */
 	build_joinrel_tlist(root, joinrel, outer_rel);
 	build_joinrel_tlist(root, joinrel, inner_rel);
+
+	/* Add any newly-computable PlaceHolderVars, too */
 	add_placeholders_to_joinrel(root, joinrel, outer_rel, inner_rel);
 
 	/*
@@ -966,6 +968,7 @@ min_join_parameterization(PlannerInfo *root,
  * The join's targetlist includes all Vars of its member relations that
  * will still be needed above the join.  This subroutine adds all such
  * Vars from the specified input rel's tlist to the join rel's tlist.
+ * Likewise for any PlaceHolderVars emitted by the input rel.
  *
  * We also compute the expected width of the join's output, making use
  * of data that was cached at the baserel level by set_rel_width().
@@ -982,11 +985,24 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 		Var		   *var = (Var *) lfirst(vars);
 
 		/*
-		 * Ignore PlaceHolderVars in the input tlists; we'll make our own
-		 * decisions about whether to copy them.
+		 * For a PlaceHolderVar, we have to look up the PlaceHolderInfo.
 		 */
 		if (IsA(var, PlaceHolderVar))
+		{
+			PlaceHolderVar *phv = (PlaceHolderVar *) var;
+			PlaceHolderInfo *phinfo = find_placeholder_info(root, phv, false);
+
+			/* Is it still needed above this joinrel? */
+			if (bms_nonempty_difference(phinfo->ph_needed, relids))
+			{
+				/* Yup, add it to the output */
+				joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
+													phv);
+				/* Bubbling up the precomputed result has cost zero */
+				joinrel->reltarget->width += phinfo->ph_width;
+			}
 			continue;
+		}
 
 		/*
 		 * Otherwise, anything in a baserel or joinrel targetlist ought to be
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index b9853af2dc..2ed2e542a4 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -5793,10 +5793,10 @@ select * from
  Nested Loop
    Output: c.q1, c.q2, a.q1, a.q2, b.q1, (COALESCE(b.q2, '42'::bigint)), d.q1, (COALESCE((COALESCE(b.q2, '42'::bigint)), d.q2)), ((COALESCE((COALESCE(b.q2, '42'::bigint)), d.q2)))
    ->  Hash Right Join
-         Output: c.q1, c.q2, a.q1, a.q2, b.q1, d.q1, (COALESCE(b.q2, '42'::bigint)), (COALESCE((COALESCE(b.q2, '42'::bigint)), d.q2))
+         Output: c.q1, c.q2, a.q1, a.q2, b.q1, (COALESCE(b.q2, '42'::bigint)), d.q1, (COALESCE((COALESCE(b.q2, '42'::bigint)), d.q2))
          Hash Cond: (d.q1 = c.q2)
          ->  Nested Loop
-               Output: a.q1, a.q2, b.q1, d.q1, (COALESCE(b.q2, '42'::bigint)), (COALESCE((COALESCE(b.q2, '42'::bigint)), d.q2))
+               Output: a.q1, a.q2, b.q1, (COALESCE(b.q2, '42'::bigint)), d.q1, (COALESCE((COALESCE(b.q2, '42'::bigint)), d.q2))
                ->  Hash Left Join
                      Output: a.q1, a.q2, b.q1, (COALESCE(b.q2, '42'::bigint))
                      Hash Cond: (a.q2 = b.q1)