diff --git a/contrib/test_decoding/expected/snapshot_build.out b/contrib/test_decoding/expected/snapshot_build.out
index 0fcf20cce86..32e5cd1dd1d 100644
--- a/contrib/test_decoding/expected/snapshot_build.out
+++ b/contrib/test_decoding/expected/snapshot_build.out
@@ -31,3 +31,100 @@ COMMIT
 stop    
 (1 row)
 
+
+starting permutation: s1_begin s1_insert s2_init s3_begin s3_insert s4_create_subxact s1_commit s4_begin s4_insert s3_commit s4_commit s2_get_changes
+step s1_begin: BEGIN;
+step s1_insert: INSERT INTO tbl1 VALUES (1);
+step s2_init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding'); <waiting ...>
+step s3_begin: BEGIN;
+step s3_insert: INSERT INTO tbl1 VALUES (1);
+step s4_create_subxact: BEGIN; SAVEPOINT a; CREATE TABLE tbl2 (val1 integer); RELEASE a; COMMIT;
+step s1_commit: COMMIT;
+step s4_begin: BEGIN;
+step s4_insert: INSERT INTO tbl2 VALUES (1);
+step s3_commit: COMMIT;
+step s2_init: <... completed>
+?column?
+--------
+init    
+(1 row)
+
+step s4_commit: COMMIT;
+step s2_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
+data                                      
+------------------------------------------
+BEGIN                                     
+table public.tbl2: INSERT: val1[integer]:1
+COMMIT                                    
+(3 rows)
+
+?column?
+--------
+stop    
+(1 row)
+
+
+starting permutation: s1_begin s1_insert s2_init s3_begin s3_insert s4_prepare s4_commit_prepared s1_commit s4_begin s4_insert s3_commit s4_commit s2_get_changes
+step s1_begin: BEGIN;
+step s1_insert: INSERT INTO tbl1 VALUES (1);
+step s2_init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding'); <waiting ...>
+step s3_begin: BEGIN;
+step s3_insert: INSERT INTO tbl1 VALUES (1);
+step s4_prepare: BEGIN; CREATE TABLE tbl2 (val1 integer); PREPARE TRANSACTION 'snapshot_build';
+step s4_commit_prepared: COMMIT PREPARED 'snapshot_build';
+step s1_commit: COMMIT;
+step s4_begin: BEGIN;
+step s4_insert: INSERT INTO tbl2 VALUES (1);
+step s3_commit: COMMIT;
+step s2_init: <... completed>
+?column?
+--------
+init    
+(1 row)
+
+step s4_commit: COMMIT;
+step s2_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
+data                                      
+------------------------------------------
+BEGIN                                     
+table public.tbl2: INSERT: val1[integer]:1
+COMMIT                                    
+(3 rows)
+
+?column?
+--------
+stop    
+(1 row)
+
+
+starting permutation: s1_begin s1_insert s2_init s3_begin s3_insert s4_alter s1_commit s4_begin s4_insert3 s3_commit s4_commit s2_get_changes
+step s1_begin: BEGIN;
+step s1_insert: INSERT INTO tbl1 VALUES (1);
+step s2_init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding'); <waiting ...>
+step s3_begin: BEGIN;
+step s3_insert: INSERT INTO tbl1 VALUES (1);
+step s4_alter: ALTER TABLE tbl3 ADD COLUMN val2 text, ADD COLUMN val3 bigint;
+step s1_commit: COMMIT;
+step s4_begin: BEGIN;
+step s4_insert3: INSERT INTO tbl3 VALUES (1, 'two', 3);
+step s3_commit: COMMIT;
+step s2_init: <... completed>
+?column?
+--------
+init    
+(1 row)
+
+step s4_commit: COMMIT;
+step s2_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
+data                                                                      
+--------------------------------------------------------------------------
+BEGIN                                                                     
+table public.tbl3: INSERT: val1[integer]:1 val2[text]:'two' val3[bigint]:3
+COMMIT                                                                    
+(3 rows)
+
+?column?
+--------
+stop    
+(1 row)
+
diff --git a/contrib/test_decoding/specs/snapshot_build.spec b/contrib/test_decoding/specs/snapshot_build.spec
index 334531dd219..65625e548ed 100644
--- a/contrib/test_decoding/specs/snapshot_build.spec
+++ b/contrib/test_decoding/specs/snapshot_build.spec
@@ -4,13 +4,16 @@ setup
 {
     DROP TABLE IF EXISTS tbl1;
     DROP TABLE IF EXISTS tbl2;
+    DROP TABLE IF EXISTS tbl3;
     CREATE TABLE tbl1 (val1 integer);
+    CREATE TABLE tbl3 (val1 integer);
 }
 
 teardown
 {
     DROP TABLE tbl1;
-    DROP TABLE tbl2;
+    DROP TABLE IF EXISTS tbl2;
+    DROP TABLE tbl3;
     SELECT 'stop' FROM pg_drop_replication_slot('isolation_slot');
 }
 
@@ -34,8 +37,13 @@ step "s3_commit" { COMMIT; }
 session "s4"
 setup { SET synchronous_commit=on; }
 step "s4_create" { CREATE TABLE tbl2 (val1 integer); }
+step "s4_create_subxact" { BEGIN; SAVEPOINT a; CREATE TABLE tbl2 (val1 integer); RELEASE a; COMMIT; }
+step "s4_prepare" { BEGIN; CREATE TABLE tbl2 (val1 integer); PREPARE TRANSACTION 'snapshot_build'; }
+step "s4_commit_prepared" { COMMIT PREPARED 'snapshot_build'; }
+step "s4_alter" { ALTER TABLE tbl3 ADD COLUMN val2 text, ADD COLUMN val3 bigint; }
 step "s4_begin" { BEGIN; }
 step "s4_insert" { INSERT INTO tbl2 VALUES (1); }
+step "s4_insert3" { INSERT INTO tbl3 VALUES (1, 'two', 3); }
 step "s4_commit" { COMMIT; }
 
 # T1: s1_begin -> s1_insert -> BUILDING_SNAPSHOT -> s1_commit -> FULL_SNAPSHOT
@@ -44,3 +52,13 @@ step "s4_commit" { COMMIT; }
 # T4: FULL_SNAPSHOT -> s4_begin -> s4_insert -> CONSISTENT -> s4_commit
 # The snapshot must track T3 or the replay of T4 will fail because its snapshot cannot see tbl2
 permutation "s1_begin" "s1_insert" "s2_init" "s3_begin" "s3_insert" "s4_create" "s1_commit" "s4_begin" "s4_insert" "s3_commit" "s4_commit" "s2_get_changes"
+
+# The same, with the catalog change made in a subtransaction.
+permutation "s1_begin" "s1_insert" "s2_init" "s3_begin" "s3_insert" "s4_create_subxact" "s1_commit" "s4_begin" "s4_insert" "s3_commit" "s4_commit" "s2_get_changes"
+
+# The same, with the catalog change committed by COMMIT PREPARED.
+permutation "s1_begin" "s1_insert" "s2_init" "s3_begin" "s3_insert" "s4_prepare" "s4_commit_prepared" "s1_commit" "s4_begin" "s4_insert" "s3_commit" "s4_commit" "s2_get_changes"
+
+# An ALTER TABLE instead: without tracking T3, the insert is decoded with the
+# old tuple descriptor and the new columns are silently dropped.
+permutation "s1_begin" "s1_insert" "s2_init" "s3_begin" "s3_insert" "s4_alter" "s1_commit" "s4_begin" "s4_insert3" "s3_commit" "s4_commit" "s2_get_changes"