diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 011bb4acddb..d8352f63273 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -20870,13 +20870,14 @@ ATExecDetachPartition(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	Relation	partRel;
 	ObjectAddress address;
 	Oid			defaultPartOid;
+	PartitionDesc partdesc;
 
 	/*
 	 * We must lock the default partition, because detaching this partition
 	 * will change its partition constraint.
 	 */
-	defaultPartOid =
-		get_default_oid_from_partdesc(RelationGetPartitionDesc(rel, true));
+	partdesc = RelationGetPartitionDesc(rel, true);
+	defaultPartOid = get_default_oid_from_partdesc(partdesc);
 	if (OidIsValid(defaultPartOid))
 	{
 		/*
@@ -20943,10 +20944,13 @@ ATExecDetachPartition(List **wqueue, AlteredTableInfo *tab, Relation rel,
 		char	   *partrelname;
 
 		/*
-		 * Add a new constraint to the partition being detached, which
-		 * supplants the partition constraint (unless there is one already).
+		 * For strategies other than hash, add a constraint to the partition
+		 * being detached which supplants the partition constraint. For hash
+		 * we cannot do that, because the constraint would reference the
+		 * partitioned table OID, possibly causing problems later.
 		 */
-		DetachAddConstraintIfNeeded(wqueue, partRel);
+		if (partdesc->boundinfo->strategy != PARTITION_STRATEGY_HASH)
+			DetachAddConstraintIfNeeded(wqueue, partRel);
 
 		/*
 		 * We're almost done now; the only traces that remain are the
diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index b33e06a0d3d..11dbb0426f1 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -4490,6 +4490,14 @@ Check constraints:
     "part_rp100_a_check" CHECK (a >= 123 AND a < 133 AND a IS NOT NULL)
 
 DROP TABLE range_parted2;
+-- Test that hash partitions continue to work after they're concurrently
+-- detached (bugs #18371, #19070)
+CREATE TABLE hash_parted2 (a int) PARTITION BY HASH(a);
+CREATE TABLE part_hp PARTITION OF hash_parted2 FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+ALTER TABLE hash_parted2 DETACH PARTITION part_hp CONCURRENTLY;
+DROP TABLE hash_parted2;
+INSERT INTO part_hp VALUES (1);
+DROP TABLE part_hp;
 -- Check ALTER TABLE commands for partitioned tables and partitions
 -- cannot add/drop column to/from *only* the parent
 ALTER TABLE ONLY list_parted2 ADD COLUMN c int;
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 90bf5c17682..f1a7d776013 100644
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -2834,6 +2834,15 @@ ALTER TABLE range_parted2 DETACH PARTITION part_rp100 CONCURRENTLY;
 \d part_rp100
 DROP TABLE range_parted2;
 
+-- Test that hash partitions continue to work after they're concurrently
+-- detached (bugs #18371, #19070)
+CREATE TABLE hash_parted2 (a int) PARTITION BY HASH(a);
+CREATE TABLE part_hp PARTITION OF hash_parted2 FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+ALTER TABLE hash_parted2 DETACH PARTITION part_hp CONCURRENTLY;
+DROP TABLE hash_parted2;
+INSERT INTO part_hp VALUES (1);
+DROP TABLE part_hp;
+
 -- Check ALTER TABLE commands for partitioned tables and partitions
 
 -- cannot add/drop column to/from *only* the parent