diff --git a/tsl/src/compression/compression_dml.c b/tsl/src/compression/compression_dml.c
index 4ac9811e23e..2083d7d4035 100644
--- a/tsl/src/compression/compression_dml.c
+++ b/tsl/src/compression/compression_dml.c
@@ -805,12 +805,13 @@ get_batch_keys_for_unique_constraints(const ChunkInsertState *cis, Relation rela
 		 */
 		for (int i = 0; i < indexDesc->rd_index->indnkeyatts; i++)
 		{
-			int attno = indexDesc->rd_index->indkey.values[i];
+			AttrNumber attno = indexDesc->rd_index->indkey.values[i];
 			/* We are not interested in expression columns which will have attno = 0 */
 			if (!attno)
 				continue;
 
-			idx_attrs = bms_add_member(idx_attrs, attno - FirstLowInvalidHeapAttributeNumber);
+			Assert(AttrNumberIsForUserDefinedAttr(attno));
+			idx_attrs = bms_add_member(idx_attrs, attno);
 		}
 		index_close(indexDesc, AccessShareLock);
 
@@ -1351,11 +1352,9 @@ key_column_is_null(tuple_filtering_constraints *constraints, Relation chunk_rel,
 	if (!constraints->covered || constraints->nullsnotdistinct)
 		return false;
 
-	int i = -1;
-	while ((i = bms_next_member(constraints->key_columns, i)) > 0)
+	AttrNumber chunk_attno = -1;
+	while ((chunk_attno = bms_next_member(constraints->key_columns, chunk_attno)) > 0)
 	{
-		AttrNumber chunk_attno = i + FirstLowInvalidHeapAttributeNumber;
-
 		/*
 		 * slot has the physical layout of the hypertable, so we need to
 		 * get the attribute number of the hypertable for the column.
diff --git a/tsl/src/compression/compression_dml.h b/tsl/src/compression/compression_dml.h
index 90133e90076..e59fef8bc47 100644
--- a/tsl/src/compression/compression_dml.h
+++ b/tsl/src/compression/compression_dml.h
@@ -13,6 +13,11 @@
 
 typedef struct tuple_filtering_constraints
 {
+	/*
+	 * All key column heap attribute numbers on uncompressed chunk.
+	 * We shouldn't be dealing with system columns so no need to
+	 * add/subtract FirstLowInvalidHeapAttributeNumber from these.
+	 */
 	Bitmapset *key_columns;
 	/*
 	 * The covered flag is set to true if we have a single constraint that is covered
diff --git a/tsl/src/compression/compression_scankey.c b/tsl/src/compression/compression_scankey.c
index 9f6c2909e6e..3ba2b5a62b5 100644
--- a/tsl/src/compression/compression_scankey.c
+++ b/tsl/src/compression/compression_scankey.c
@@ -45,10 +45,9 @@ build_mem_scankeys_from_slot(Oid ht_relid, CompressionSettings *settings, Relati
 
 	scankeys = palloc(sizeof(ScanKeyData) * bms_num_members(constraints->key_columns));
 
-	int i = -1;
-	while ((i = bms_next_member(constraints->key_columns, i)) > 0)
+	AttrNumber attno = -1;
+	while ((attno = bms_next_member(constraints->key_columns, attno)) > 0)
 	{
-		AttrNumber attno = i + FirstLowInvalidHeapAttributeNumber;
 		bool isnull;
 
 		/*
@@ -125,10 +124,9 @@ build_heap_scankeys(Oid hypertable_relid, Relation in_rel, Relation out_rel,
 	if (!bms_is_empty(key_columns))
 	{
 		scankeys = palloc0(bms_num_members(key_columns) * 2 * sizeof(ScanKeyData));
-		int i = -1;
-		while ((i = bms_next_member(key_columns, i)) > 0)
+		AttrNumber attno = -1;
+		while ((attno = bms_next_member(key_columns, attno)) > 0)
 		{
-			AttrNumber attno = i + FirstLowInvalidHeapAttributeNumber;
 			char *attname = get_attname(out_rel->rd_id, attno, false);
 			bool isnull;
 			AttrNumber ht_attno = get_attnum(hypertable_relid, attname);
@@ -322,8 +320,7 @@ build_index_scankeys_using_slot(Oid hypertable_relid, Relation in_rel, Relation
 			AttrNumber idx_attnum = AttrOffsetGetAttrNumber(i);
 			AttrNumber in_attnum = index_rel->rd_index->indkey.values[i];
 			const NameData *attname = attnumAttName(in_rel, in_attnum);
-			AttrNumber column_attno =
-				get_attnum(out_rel->rd_id, NameStr(*attname)) - FirstLowInvalidHeapAttributeNumber;
+			AttrNumber column_attno = get_attnum(out_rel->rd_id, NameStr(*attname));
 
 			/* Make sure we find columns in key columns in order to select the right index */
 			if (!bms_is_member(column_attno, key_columns))