diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 0866a680d7c..af87807fa30 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -17462,22 +17462,31 @@ ATExecDetachPartition(Relation rel, RangeVar *name)
 	foreach(cell, indexes)
 	{
 		Oid			idxid = lfirst_oid(cell);
+		Oid			parentidx;
 		Relation	idx;
 		Oid			constrOid;
+		Oid			parentConstrOid;
 
 		if (!has_superclass(idxid))
 			continue;
 
-		Assert((IndexGetRelation(get_partition_parent(idxid), false) ==
-				RelationGetRelid(rel)));
+		parentidx = get_partition_parent(idxid);
+		Assert(IndexGetRelation(parentidx, false) == RelationGetRelid(rel));
 
 		idx = index_open(idxid, AccessExclusiveLock);
 		IndexSetParentIndex(idx, InvalidOid);
 
-		/* If there's a constraint associated with the index, detach it too */
+		/*
+		 * If there's a constraint associated with the index, detach it too.
+		 * Careful: it is possible for a constraint index in a partition to be
+		 * the child of a non-constraint index, so verify whether the parent
+		 * index does actually have a constraint.
+		 */
 		constrOid = get_relation_idx_constraint_oid(RelationGetRelid(partRel),
 													idxid);
-		if (OidIsValid(constrOid))
+		parentConstrOid = get_relation_idx_constraint_oid(RelationGetRelid(rel),
+														  parentidx);
+		if (OidIsValid(parentConstrOid) && OidIsValid(constrOid))
 			ConstraintSetParentConstraint(constrOid, InvalidOid, InvalidOid);
 
 		index_close(idx, NoLock);
diff --git a/src/test/regress/expected/sanity_check.out b/src/test/regress/expected/sanity_check.out
index 3e05efd7b5b..723c270ba26 100644
--- a/src/test/regress/expected/sanity_check.out
+++ b/src/test/regress/expected/sanity_check.out
@@ -172,6 +172,8 @@ quad_poly_tbl|t
 radix_text_tbl|t
 ramp|f
 real_city|f
+regress_constr_partition1|t
+regress_constr_partitioned|t
 road|t
 shighway|t
 slow_emp4000|f
diff --git a/src/test/regress/input/constraints.source b/src/test/regress/input/constraints.source
index d7996a5d837..47f2bfa0b4f 100644
--- a/src/test/regress/input/constraints.source
+++ b/src/test/regress/input/constraints.source
@@ -429,6 +429,46 @@ ALTER TABLE parted_fk_naming ATTACH PARTITION parted_fk_naming_1 FOR VALUES IN (
 SELECT conname FROM pg_constraint WHERE conrelid = 'parted_fk_naming_1'::regclass AND contype = 'f';
 DROP TABLE parted_fk_naming;
 
+--
+-- Test various ways to create primary keys on partitions, linked to unique
+-- indexes (without constraints) on the partitioned table.  Ideally these should
+-- fail, but we don't dare change released behavior, so instead cope with it at
+-- DETACH time.
+CREATE TEMP TABLE t (a integer, b integer) PARTITION BY HASH (a, b);
+CREATE TEMP TABLE tp (a integer, b integer, PRIMARY KEY (a, b), UNIQUE (b, a));
+ALTER TABLE t ATTACH PARTITION tp FOR VALUES WITH (MODULUS 1, REMAINDER 0);
+CREATE UNIQUE INDEX t_a_idx ON t (a, b);
+CREATE UNIQUE INDEX t_b_idx ON t (b, a);
+ALTER INDEX t_a_idx ATTACH PARTITION tp_pkey;
+ALTER INDEX t_b_idx ATTACH PARTITION tp_b_a_key;
+ALTER TABLE t DETACH PARTITION tp;
+SELECT conname, conparentid, conislocal, coninhcount
+  FROM pg_constraint WHERE conname IN ('tp_pkey', 'tp_b_a_key');
+DROP TABLE t, tp;
+
+CREATE TEMP TABLE t (a integer) PARTITION BY LIST (a);
+CREATE TEMP TABLE tp (a integer PRIMARY KEY);
+CREATE UNIQUE INDEX t_a_idx ON t (a);
+ALTER TABLE t ATTACH PARTITION tp FOR VALUES IN (1);
+ALTER TABLE t DETACH PARTITION tp;
+DROP TABLE t, tp;
+
+CREATE TEMP TABLE t (a integer) PARTITION BY LIST (a);
+CREATE TEMP TABLE tp (a integer PRIMARY KEY);
+CREATE UNIQUE INDEX t_a_idx ON ONLY t (a);
+ALTER TABLE t ATTACH PARTITION tp FOR VALUES IN (1);
+ALTER TABLE t DETACH PARTITION tp;
+DROP TABLE t, tp;
+
+CREATE TABLE regress_constr_partitioned (a integer) PARTITION BY LIST (a);
+CREATE TABLE regress_constr_partition1 PARTITION OF regress_constr_partitioned FOR VALUES IN (1);
+ALTER TABLE regress_constr_partition1 ADD PRIMARY KEY (a);
+CREATE UNIQUE INDEX ON regress_constr_partitioned (a);
+BEGIN;
+ALTER TABLE regress_constr_partitioned DETACH PARTITION regress_constr_partition1;
+ROLLBACK;
+--  Leave this one in funny state for pg_upgrade testing
+
 -- test a HOT update that invalidates the conflicting tuple.
 -- the trigger should still fire and catch the violation
 
diff --git a/src/test/regress/output/constraints.source b/src/test/regress/output/constraints.source
index 5d60451b9a1..d0cbc70b1a6 100644
--- a/src/test/regress/output/constraints.source
+++ b/src/test/regress/output/constraints.source
@@ -598,6 +598,48 @@ SELECT conname FROM pg_constraint WHERE conrelid = 'parted_fk_naming_1'::regclas
 (1 row)
 
 DROP TABLE parted_fk_naming;
+--
+-- Test various ways to create primary keys on partitions, linked to unique
+-- indexes (without constraints) on the partitioned table.  Ideally these should
+-- fail, but we don't dare change released behavior, so instead cope with it at
+-- DETACH time.
+CREATE TEMP TABLE t (a integer, b integer) PARTITION BY HASH (a, b);
+CREATE TEMP TABLE tp (a integer, b integer, PRIMARY KEY (a, b), UNIQUE (b, a));
+ALTER TABLE t ATTACH PARTITION tp FOR VALUES WITH (MODULUS 1, REMAINDER 0);
+CREATE UNIQUE INDEX t_a_idx ON t (a, b);
+CREATE UNIQUE INDEX t_b_idx ON t (b, a);
+ALTER INDEX t_a_idx ATTACH PARTITION tp_pkey;
+ALTER INDEX t_b_idx ATTACH PARTITION tp_b_a_key;
+ALTER TABLE t DETACH PARTITION tp;
+SELECT conname, conparentid, conislocal, coninhcount
+  FROM pg_constraint WHERE conname IN ('tp_pkey', 'tp_b_a_key');
+  conname   | conparentid | conislocal | coninhcount 
+------------+-------------+------------+-------------
+ tp_pkey    |           0 | t          |           0
+ tp_b_a_key |           0 | t          |           0
+(2 rows)
+
+DROP TABLE t, tp;
+CREATE TEMP TABLE t (a integer) PARTITION BY LIST (a);
+CREATE TEMP TABLE tp (a integer PRIMARY KEY);
+CREATE UNIQUE INDEX t_a_idx ON t (a);
+ALTER TABLE t ATTACH PARTITION tp FOR VALUES IN (1);
+ALTER TABLE t DETACH PARTITION tp;
+DROP TABLE t, tp;
+CREATE TEMP TABLE t (a integer) PARTITION BY LIST (a);
+CREATE TEMP TABLE tp (a integer PRIMARY KEY);
+CREATE UNIQUE INDEX t_a_idx ON ONLY t (a);
+ALTER TABLE t ATTACH PARTITION tp FOR VALUES IN (1);
+ALTER TABLE t DETACH PARTITION tp;
+DROP TABLE t, tp;
+CREATE TABLE regress_constr_partitioned (a integer) PARTITION BY LIST (a);
+CREATE TABLE regress_constr_partition1 PARTITION OF regress_constr_partitioned FOR VALUES IN (1);
+ALTER TABLE regress_constr_partition1 ADD PRIMARY KEY (a);
+CREATE UNIQUE INDEX ON regress_constr_partitioned (a);
+BEGIN;
+ALTER TABLE regress_constr_partitioned DETACH PARTITION regress_constr_partition1;
+ROLLBACK;
+--  Leave this one in funny state for pg_upgrade testing
 -- test a HOT update that invalidates the conflicting tuple.
 -- the trigger should still fire and catch the violation
 BEGIN;