diff --git a/src/lib-index/mail-index-map-hdr.c b/src/lib-index/mail-index-map-hdr.c
index 59b0c7f93d..1caa3f1a2e 100644
--- a/src/lib-index/mail-index-map-hdr.c
+++ b/src/lib-index/mail-index-map-hdr.c
@@ -293,7 +293,7 @@ int mail_index_map_check_header(struct mail_index_map *map,
 		/* pre-v2.2 (although should have been done in v2.1 already):
 		   make sure the old unused fields are cleared */
 		map->hdr.unused_old_sync_size = 0;
-		map->hdr.unused_old_sync_stamp = 0;
+		map->hdr.last_temp_file_scan = 0;
 	}
 	if (hdr->first_recent_uid == 0) {
 		*error_r = "first_recent_uid=0";
diff --git a/src/lib-index/mail-index.h b/src/lib-index/mail-index.h
index 1dde6c5f3e..b6434f7a68 100644
--- a/src/lib-index/mail-index.h
+++ b/src/lib-index/mail-index.h
@@ -106,7 +106,7 @@ struct mail_index_header {
 	uint32_t log_file_head_offset;
 
 	uint64_t unused_old_sync_size;
-	uint32_t unused_old_sync_stamp;
+	uint32_t last_temp_file_scan;
 
 	/* daily first UIDs that have been added to index. */
 	uint32_t day_stamp;
diff --git a/src/lib-storage/index/index-storage.c b/src/lib-storage/index/index-storage.c
index 67493497cf..55904b5c22 100644
--- a/src/lib-storage/index/index-storage.c
+++ b/src/lib-storage/index/index-storage.c
@@ -861,6 +861,22 @@ int index_storage_mailbox_rename(struct mailbox *src, struct mailbox *dest)
 	return 0;
 }
 
+int index_mailbox_update_last_temp_file_scan(struct mailbox *box)
+{
+	uint32_t last_temp_file_scan = ioloop_time;
+	struct mail_index_transaction *trans =
+		mail_index_transaction_begin(box->view,
+			MAIL_INDEX_TRANSACTION_FLAG_EXTERNAL);
+	mail_index_update_header(trans,
+		offsetof(struct mail_index_header, last_temp_file_scan),
+		&last_temp_file_scan, sizeof(last_temp_file_scan), TRUE);
+	if (mail_index_transaction_commit(&trans) < 0) {
+		mailbox_set_index_error(box);
+		return -1;
+	}
+	return 0;
+}
+
 bool index_storage_is_readonly(struct mailbox *box)
 {
 	return (box->flags & MAILBOX_FLAG_READONLY) != 0;
diff --git a/src/lib-storage/index/index-storage.h b/src/lib-storage/index/index-storage.h
index ff5ed4c1cf..9218e1ac65 100644
--- a/src/lib-storage/index/index-storage.h
+++ b/src/lib-storage/index/index-storage.h
@@ -80,6 +80,8 @@ int index_storage_mailbox_delete(struct mailbox *box);
 int index_storage_mailbox_delete_dir(struct mailbox *box, bool mailbox_deleted);
 int index_storage_mailbox_rename(struct mailbox *src, struct mailbox *dest);
 
+int index_mailbox_update_last_temp_file_scan(struct mailbox *box);
+
 bool index_storage_is_readonly(struct mailbox *box);
 bool index_storage_is_inconsistent(struct mailbox *box);