diff --git a/schemas/ispyb/updates/2024_03_05_BLSubSample_replace_index.sql b/schemas/ispyb/updates/2024_03_05_BLSubSample_replace_index.sql
new file mode 100644
index 00000000..3381948c
--- /dev/null
+++ b/schemas/ispyb/updates/2024_03_05_BLSubSample_replace_index.sql
@@ -0,0 +1,6 @@
+INSERT IGNORE INTO SchemaStatus (scriptName, schemaStatus) VALUES ('2024_03_05_BLSubSample_replace_index.sql', 'ONGOING');
+
+CREATE INDEX IF NOT EXISTS BLSubSample_blSampleId_source ON BLSubSample(blSampleId, source);
+DROP INDEX IF EXISTS BLSubSample_FKIndex1 ON BLSubSample;
+
+UPDATE SchemaStatus SET schemaStatus = 'DONE' WHERE scriptName = '2024_03_05_BLSubSample_replace_index.sql';