diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 52ebdd90fcb..5a0ecd80a07 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -4436,10 +4436,24 @@ cost_subplan(PlannerInfo *root, SubPlan *subplan, Plan *plan)
 {
 	QualCost	sp_cost;
 
-	/* Figure any cost for evaluating the testexpr */
+	/*
+	 * Figure any cost for evaluating the testexpr.
+	 *
+	 * Usually, SubPlan nodes are built very early, before we have constructed
+	 * any RelOptInfos for the parent query level, which means the parent root
+	 * does not yet contain enough information to safely consult statistics.
+	 * Therefore, we pass root as NULL here.  cost_qual_eval() is already
+	 * well-equipped to handle a NULL root.
+	 *
+	 * One exception is SubPlan nodes built for the initplans of MIN/MAX
+	 * aggregates from indexes (cf. SS_make_initplan_from_plan).  In this
+	 * case, having a NULL root is safe because testexpr will be NULL.
+	 * Besides, an initplan will by definition not consult anything from the
+	 * parent plan.
+	 */
 	cost_qual_eval(&sp_cost,
 				   make_ands_implicit((Expr *) subplan->testexpr),
-				   root);
+				   NULL);
 
 	if (subplan->useHashTable)
 	{
diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index 6c1fb2bfdbb..e41d31b3084 100644
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -773,6 +773,25 @@ select (select (a.*)::text) from view_a a;
  (42)
 (1 row)
 
+--
+-- Test case for bug #19037: no relation entry for relid N
+--
+explain (costs off)
+select (1 = any(array_agg(f1))) = any (select false) from int4_tbl;
+         QUERY PLAN         
+----------------------------
+ Aggregate
+   ->  Seq Scan on int4_tbl
+   SubPlan 1
+     ->  Result
+(4 rows)
+
+select (1 = any(array_agg(f1))) = any (select false) from int4_tbl;
+ ?column? 
+----------
+ t
+(1 row)
+
 --
 -- Check that whole-row Vars reading the result of a subselect don't include
 -- any junk columns therein
diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index e5a562c3f5d..fb0a901a516 100644
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -412,6 +412,15 @@ select (select view_a) from view_a;
 select (select (select view_a)) from view_a;
 select (select (a.*)::text) from view_a a;
 
+--
+-- Test case for bug #19037: no relation entry for relid N
+--
+
+explain (costs off)
+select (1 = any(array_agg(f1))) = any (select false) from int4_tbl;
+
+select (1 = any(array_agg(f1))) = any (select false) from int4_tbl;
+
 --
 -- Check that whole-row Vars reading the result of a subselect don't include
 -- any junk columns therein