diff --git a/contrib/test_decoding/expected/repack.out b/contrib/test_decoding/expected/repack.out
index 0d229050146..e7060a7e577 100644
--- a/contrib/test_decoding/expected/repack.out
+++ b/contrib/test_decoding/expected/repack.out
@@ -51,6 +51,22 @@ SELECT * FROM rpk_missing;
 (3 rows)
 
 DROP TABLE rpk_missing;
+-- Verify handling of !indisready indexes
+CREATE TABLE repack_conc_invidx (i int PRIMARY KEY, j int);
+INSERT INTO repack_conc_invidx VALUES (1, 0), (2, 0);
+CREATE UNIQUE INDEX CONCURRENTLY repack_conc_invidx_uq ON repack_conc_invidx (j);
+ERROR:  could not create unique index "repack_conc_invidx_uq"
+DETAIL:  Key (j)=(0) is duplicated.
+CREATE INDEX CONCURRENTLY repack_conc_invalid_expr ON repack_conc_invidx ((1/j));
+ERROR:  division by zero
+REPACK repack_conc_invidx;
+ERROR:  cannot execute REPACK on relation "repack_conc_invidx"
+DETAIL:  Some invalid indexes cannot be processed correctly: "repack_conc_invidx_uq", "repack_conc_invalid_expr".
+HINT:  Use DROP INDEX or REINDEX.
+REPACK (CONCURRENTLY) repack_conc_invidx;
+ERROR:  cannot execute REPACK on relation "repack_conc_invidx"
+DETAIL:  Some invalid indexes cannot be processed correctly: "repack_conc_invidx_uq", "repack_conc_invalid_expr".
+HINT:  Use DROP INDEX or REINDEX.
 -- Error cases for concurrent mode
 -- Doesn't like partitioned tables
 CREATE TABLE clstrpart (a int) PARTITION BY RANGE (a);
diff --git a/contrib/test_decoding/sql/repack.sql b/contrib/test_decoding/sql/repack.sql
index 6e51aedb72d..0107e0bf89d 100644
--- a/contrib/test_decoding/sql/repack.sql
+++ b/contrib/test_decoding/sql/repack.sql
@@ -33,6 +33,14 @@ REPACK (CONCURRENTLY) rpk_missing;
 SELECT * FROM rpk_missing;
 DROP TABLE rpk_missing;
 
+-- Verify handling of !indisready indexes
+CREATE TABLE repack_conc_invidx (i int PRIMARY KEY, j int);
+INSERT INTO repack_conc_invidx VALUES (1, 0), (2, 0);
+CREATE UNIQUE INDEX CONCURRENTLY repack_conc_invidx_uq ON repack_conc_invidx (j);
+CREATE INDEX CONCURRENTLY repack_conc_invalid_expr ON repack_conc_invidx ((1/j));
+REPACK repack_conc_invidx;
+REPACK (CONCURRENTLY) repack_conc_invidx;
+
 -- Error cases for concurrent mode
 
 -- Doesn't like partitioned tables
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 83168a4e6f3..609e2c1d77e 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -159,6 +159,7 @@ static bool cluster_rel_recheck(RepackCommand cmd, Relation OldHeap,
 								int options);
 static void check_concurrent_repack_requirements(Relation rel,
 												 Oid *ident_idx_p);
+static void check_index_requirements(Relation rel, RepackCommand cmd);
 static void rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 							 Oid ident_idx);
 static void copy_table_data(Relation NewHeap, Relation OldHeap, Relation OldIndex,
@@ -527,6 +528,14 @@ cluster_rel(RepackCommand cmd, Relation OldHeap, Oid indexOid,
 	if (concurrent)
 		check_concurrent_repack_requirements(OldHeap, &ident_idx);
 
+	/*
+	 * Also check the state of indexes; this can abort the command for REPACK.
+	 * Historically this hasn't affected CLUSTER or VACUUM FULL, so don't do
+	 * it for those commands.
+	 */
+	if (cmd == REPACK_COMMAND_REPACK)
+		check_index_requirements(OldHeap, cmd);
+
 	/* Check for user-requested abort. */
 	CHECK_FOR_INTERRUPTS();
 
@@ -874,6 +883,68 @@ mark_index_clustered(Relation rel, Oid indexOid, bool is_internal)
 	table_close(pg_index, RowExclusiveLock);
 }
 
+/*
+ * check_index_requirements: verify index state on relation being processed
+ *
+ * Throw an error if any !indisready indexes are found.
+ *
+ * Indexes that are not ready for inserts, such as ones left behind by failed
+ * CREATE INDEX CONCURRENTLY, are not maintained by DML.  In some cases they
+ * may fail to build altogether.  Throwing an error here forces the user to
+ * take action on these indexes separately from the table reconstruction,
+ * which prevents perpetuating them for no reason.
+ */
+static void
+check_index_requirements(Relation rel, RepackCommand cmd)
+{
+	Relation	indrel;
+	SysScanDesc indscan;
+	ScanKeyData skey;
+	HeapTuple	htup;
+	int			num_invalid_idxs = 0;
+	StringInfoData dest;
+
+	initStringInfo(&dest);
+
+	/* Prepare to scan pg_index for entries having indrelid = this rel. */
+	ScanKeyInit(&skey,
+				Anum_pg_index_indrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationGetRelid(rel)));
+
+	indrel = table_open(IndexRelationId, AccessShareLock);
+	indscan = systable_beginscan(indrel, IndexIndrelidIndexId, true,
+								 NULL, 1, &skey);
+
+	while (HeapTupleIsValid(htup = systable_getnext(indscan)))
+	{
+		Form_pg_index index = (Form_pg_index) GETSTRUCT(htup);
+
+		if (!index->indisready)
+		{
+			Assert(!index->indisvalid);
+			if (num_invalid_idxs == 0)
+				appendStringInfo(&dest, _("\"%s\""), get_rel_name(index->indexrelid));
+			else
+				appendStringInfo(&dest, _(", \"%s\""), get_rel_name(index->indexrelid));
+			num_invalid_idxs++;
+		}
+	}
+	systable_endscan(indscan);
+	table_close(indrel, AccessShareLock);
+
+	if (num_invalid_idxs > 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("cannot execute %s on relation \"%s\"",
+					   RepackCommandAsString(cmd), RelationGetRelationName(rel)),
+				errdetail_plural("An invalid index cannot be processed correctly: %s.",
+								 "Some invalid indexes cannot be processed correctly: %s.",
+								 num_invalid_idxs,
+								 dest.data),
+				errhint("Use DROP INDEX or REINDEX."));
+}
+
 /*
  * Check if the CONCURRENTLY option is legal for the relation.
  *