diff --git a/CHANGELOG.md b/CHANGELOG.md
index bc052c75385..94fa0926700 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,11 @@
 `psql` with the `-X` flag to prevent any `.psqlrc` commands from
 accidentally triggering the load of a previous DB version.**
 
+## Unreleased
+
+**Bugfixes**
+* #3654 Fix index attnum mapping in reorder_chunk
+
 ## 2.4.2 (2021-09-21)
 
 This release contains bug fixes since the 2.4.1 release.
diff --git a/src/chunk_index.c b/src/chunk_index.c
index 8ed9e251cb5..04382f11ddd 100644
--- a/src/chunk_index.c
+++ b/src/chunk_index.c
@@ -207,12 +207,24 @@ chunk_relation_index_create(Relation htrel, Relation template_indexrel, Relation
 {
 	IndexInfo *indexinfo = BuildIndexInfo(template_indexrel);
 	int32 hypertable_id;
+	bool skip_mapping = false;
+
+	/*
+	 * If the supplied template index is not on the hypertable we must not do attnum
+	 * mapping based on the hypertable. Ideally we would check for the template being
+	 * on the chunk but we cannot do that since when we rebuild a chunk the new chunk
+	 * has a different id. But the template index should always be either on the
+	 * hypertable or on a relation with the same physical layout as chunkrel.
+	 */
+	if (IndexGetRelation(template_indexrel->rd_id, false) != htrel->rd_id)
+		skip_mapping = true;
 
 	/*
 	 * Convert the IndexInfo's attnos to match the chunk instead of the
 	 * hypertable
 	 */
-	if (chunk_index_need_attnos_adjustment(RelationGetDescr(htrel), RelationGetDescr(chunkrel)))
+	if (!skip_mapping &&
+		chunk_index_need_attnos_adjustment(RelationGetDescr(htrel), RelationGetDescr(chunkrel)))
 		ts_adjust_indexinfo_attnos(indexinfo, htrel->rd_id, chunkrel);
 
 	hypertable_id = ts_hypertable_relid_to_id(htrel->rd_id);
diff --git a/tsl/test/expected/reorder.out b/tsl/test/expected/reorder.out
index 5456b1fa018..da13c4f35a7 100644
--- a/tsl/test/expected/reorder.out
+++ b/tsl/test/expected/reorder.out
@@ -1344,3 +1344,20 @@ WHERE indisclustered = true ORDER BY 1;
 SELECT reorder_chunk('_timescaledb_internal._hyper_2_3_chunk', verbose => TRUE);
 ERROR:  must be owner of hypertable "ct2"
 \set ON_ERROR_STOP 1
+-- #3651 incorrect index attribute mapping in reorder_chunk
+CREATE TABLE i3651(c1 timestamptz NOT NULL,c2 text, c3 text, c4 text);
+SELECT table_name FROM create_hypertable('i3651','c1');
+ table_name 
+------------
+ i3651
+(1 row)
+
+ALTER TABLE i3651 drop column c2;
+CREATE UNIQUE INDEX i3651_attmap ON i3651(c1,c4);
+INSERT INTO i3651 VALUES('2000-01-01','foo','foo'),('2000-01-01','foo','bar');
+SELECT reorder_chunk(chunk,'i3651_attmap') from show_chunks('i3651') chunk;
+ reorder_chunk 
+---------------
+ 
+(1 row)
+
diff --git a/tsl/test/sql/reorder.sql b/tsl/test/sql/reorder.sql
index 73d410955c8..252762bbc91 100644
--- a/tsl/test/sql/reorder.sql
+++ b/tsl/test/sql/reorder.sql
@@ -245,3 +245,12 @@ WHERE indisclustered = true ORDER BY 1;
 \set ON_ERROR_STOP 0
 SELECT reorder_chunk('_timescaledb_internal._hyper_2_3_chunk', verbose => TRUE);
 \set ON_ERROR_STOP 1
+
+-- #3651 incorrect index attribute mapping in reorder_chunk
+CREATE TABLE i3651(c1 timestamptz NOT NULL,c2 text, c3 text, c4 text);
+SELECT table_name FROM create_hypertable('i3651','c1');
+ALTER TABLE i3651 drop column c2;
+CREATE UNIQUE INDEX i3651_attmap ON i3651(c1,c4);
+INSERT INTO i3651 VALUES('2000-01-01','foo','foo'),('2000-01-01','foo','bar');
+SELECT reorder_chunk(chunk,'i3651_attmap') from show_chunks('i3651') chunk;
+