diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 1085d0d5b8d..ffed63a2986 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -1348,8 +1348,8 @@ CopyRelationTo(CopyToState cstate, Relation rel, Relation root_rel, uint64 *proc
 	if (root_rel != NULL)
 	{
 		root_slot = table_slot_create(root_rel, NULL);
-		map = build_attrmap_by_name_if_req(RelationGetDescr(root_rel),
-										   RelationGetDescr(rel),
+		map = build_attrmap_by_name_if_req(RelationGetDescr(rel),
+										   RelationGetDescr(root_rel),
 										   false);
 	}
 
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index 1714faab39c..37498cdd6e7 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -594,3 +594,14 @@ id	val
 5	15
 6	16
 DROP TABLE PP;
+-- Check if COPY TO handles dropped columns in partitions.
+CREATE TABLE pp_dropcol (id int, val int) PARTITION BY RANGE (id);
+CREATE TABLE pp_dropcol_1 (dropme int, id int, val int);
+ALTER TABLE pp_dropcol_1 DROP COLUMN dropme;
+ALTER TABLE pp_dropcol ATTACH PARTITION pp_dropcol_1 FOR VALUES FROM (1) TO (10);
+INSERT INTO pp_dropcol VALUES (1, 11), (2, 12);
+COPY pp_dropcol TO stdout(header);
+id	val
+1	11
+2	12
+DROP TABLE pp_dropcol;
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index eaad290b257..094fd76c12b 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -535,3 +535,12 @@ CREATE TABLE pp_510 PARTITION OF pp_2 FOR VALUES FROM (5) TO (10);
 INSERT INTO pp SELECT g, 10 + g FROM generate_series(1,6) g;
 COPY pp TO stdout(header);
 DROP TABLE PP;
+
+-- Check if COPY TO handles dropped columns in partitions.
+CREATE TABLE pp_dropcol (id int, val int) PARTITION BY RANGE (id);
+CREATE TABLE pp_dropcol_1 (dropme int, id int, val int);
+ALTER TABLE pp_dropcol_1 DROP COLUMN dropme;
+ALTER TABLE pp_dropcol ATTACH PARTITION pp_dropcol_1 FOR VALUES FROM (1) TO (10);
+INSERT INTO pp_dropcol VALUES (1, 11), (2, 12);
+COPY pp_dropcol TO stdout(header);
+DROP TABLE pp_dropcol;