diff --git a/taca/illumina/NovaSeqXPlus_Runs.py b/taca/illumina/NovaSeqXPlus_Runs.py
index 7bcde2c4..41cb4094 100644
--- a/taca/illumina/NovaSeqXPlus_Runs.py
+++ b/taca/illumina/NovaSeqXPlus_Runs.py
@@ -106,7 +106,7 @@ def _generate_samplesheet_subset(
                             noindex_flag = True
                         if field == "index2" and noindex_flag:
                             line[field] = (
-                                "A" * index_cycles[1] if index_cycles[1] != 0 else ""
+                                "T" * index_cycles[1] if index_cycles[1] != 0 else ""
                             )
                             noindex_flag = False
                         # Case of IDT UMI