diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 0ab4014..9f9a4d1 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -56,8 +56,8 @@
 typedef struct
 {
 	PlannerInfo *root;
-	int			nappinfos;
-	AppendRelInfo **appinfos;
+	int			nappinfos;	/* # of entries in appinfos array. */
+	AppendRelInfo **appinfos;	/* AppendRelInfo dectating the adjustment. */
 } adjust_appendrel_attrs_context;
 
 static RelOptInfo *recurse_set_operations(Node *setOp, PlannerInfo *root,
@@ -2037,6 +2037,9 @@ translate_col_privs(const Bitmapset *parent_privs,
  *	  update rtindexes appearing outside Vars, such as resultRelation and
  *	  jointree relids.
  *
+ * appinfos is an array of nappinfos AppendRelInfos indicating non-overlapping
+ * parent-child pairs.
+ *
  * Note: this is only applied after conversion of sublinks to subplans,
  * so we don't need to cope with recursion into sub-queries.
  *
@@ -2050,6 +2053,12 @@ adjust_appendrel_attrs(PlannerInfo *root, Node *node, int nappinfos,
 	Node	   *result;
 	adjust_appendrel_attrs_context context;
 
+#ifdef USE_ASSERT_CHECKING
+	Relids		parents = NULL;
+	Relids		children = NULL;
+	int			cnt;
+#endif /* USE_ASSERT_CHECKING */
+
 	context.root = root;
 	context.nappinfos = nappinfos;
 	context.appinfos = appinfos;
@@ -2057,6 +2066,38 @@ adjust_appendrel_attrs(PlannerInfo *root, Node *node, int nappinfos,
 	/* If there's nothing to adjust, don't call this function. */
 	Assert(nappinfos >= 1 && appinfos != NULL);
 
+#ifdef USE_ASSERT_CHECKING
+	/*
+	 * The appinfos are expected to contains non-overlapping AppendRelInfos so
+	 * that the changes made for one AppendRelInfo doesn't get affected by
+	 * another AppendRelInfo in that array. These tests are applicable only in
+	 * case of multiple AppendRelInfos.
+	 */
+	if (nappinfos > 1)
+	{
+		for (cnt = 0; cnt < nappinfos; cnt++)
+		{
+			AppendRelInfo *appinfo = appinfos[cnt];
+
+			parents = bms_add_member(parents, appinfo->parent_relid);
+			children = bms_add_member(children, appinfo->child_relid);
+		}
+
+		/* No two AppendRelInfos should have same parent or child. */
+		Assert(bms_num_members(parents) == nappinfos);
+		Assert(bms_num_members(children) == nappinfos);
+
+		/* No child should act as parent as well and vice versa. */
+		for (cnt = 0; cnt < nappinfos; cnt++)
+		{
+			AppendRelInfo *appinfo = appinfos[cnt];
+
+			Assert(!bms_is_member(appinfo->child_relid, parents));
+			Assert(!bms_is_member(appinfo->parent_relid, children));
+		}
+	}
+#endif /* USE_ASSERT_CHECKING */
+
 	/*
 	 * Must be prepared to start with a Query or a bare expression tree.
 	 */
@@ -2613,6 +2654,9 @@ build_child_join_sjinfo(PlannerInfo *root, SpecialJoinInfo *parent_sjinfo,
  *
  * The AppendRelInfos are returned in an array, which can be pfree'd by the
  * caller. *nappinfos is set to the number of entries in the array.
+ *
+ * The returned array and *nappinfos is usually passed down to
+ * adjust_appendrel_attrs(). See prologue of that function for more details.
  */
 AppendRelInfo **
 find_appinfos_by_relids(PlannerInfo *root, Relids relids, int *nappinfos)
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 3b28d19..0d17999 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -2096,6 +2096,13 @@ typedef struct SpecialJoinInfo
  * will not have many different append parents, it doesn't seem worthwhile
  * to complicate things.
  *
+ * We expand multi-level partitioning hierarchy into corresponding inheritance
+ * hierarchy level by level. An intermediate partitioned partition acts as
+ * both, a parent (of its partitions) and a child (to the partitioned table
+ * whose partition it is). Per expand_single_inheritance_child() the
+ * AppendRelInfo of an intermediate parent appears before that of any of its
+ * children.
+ *
  * Note: after completion of the planner prep phase, any given RTE is an
  * append parent having entries in append_rel_list if and only if its
  * "inh" flag is set.  We clear "inh" for plain tables that turn out not