diff --git a/src/lib-index/mail-index-transaction-update.c b/src/lib-index/mail-index-transaction-update.c
index 3a160d3bc8..a578ca7c9d 100644
--- a/src/lib-index/mail-index-transaction-update.c
+++ b/src/lib-index/mail-index-transaction-update.c
@@ -194,6 +194,14 @@ void mail_index_append(struct mail_index_transaction *t, uint32_t uid,
 void mail_index_append_finish_uids(struct mail_index_transaction *t,
 				   uint32_t first_uid,
 				   ARRAY_TYPE(seq_range) *uids_r)
+{
+	return mail_index_append_finish_uids_full(t, first_uid, first_uid, uids_r);
+}
+
+void mail_index_append_finish_uids_full(struct mail_index_transaction *t,
+					uint32_t min_allowed_uid,
+					uint32_t first_new_uid,
+					ARRAY_TYPE(seq_range) *uids_r)
 {
 	struct mail_index_record *recs;
 	unsigned int i, count;
@@ -203,13 +211,14 @@ void mail_index_append_finish_uids(struct mail_index_transaction *t,
 	if (!array_is_created(&t->appends))
 		return;
 
-	i_assert(first_uid < (uint32_t)-1);
+	i_assert(min_allowed_uid <= first_new_uid);
+	i_assert(first_new_uid < (uint32_t)-1);
 
 	/* first find the highest assigned uid */
 	recs = array_get_modifiable(&t->appends, &count);
 	i_assert(count > 0);
 
-	next_uid = first_uid;
+	next_uid = first_new_uid;
 	for (i = 0; i < count; i++) {
 		if (next_uid <= recs[i].uid)
 			next_uid = recs[i].uid + 1;
@@ -218,7 +227,7 @@ void mail_index_append_finish_uids(struct mail_index_transaction *t,
 
 	/* assign missing uids */
 	for (i = 0; i < count; i++) {
-		if (recs[i].uid == 0 || recs[i].uid < first_uid) {
+		if (recs[i].uid == 0 || recs[i].uid < min_allowed_uid) {
 			i_assert(next_uid < (uint32_t)-1);
 			recs[i].uid = next_uid++;
 			if (t->highest_append_uid < recs[i].uid)
diff --git a/src/lib-index/mail-index.h b/src/lib-index/mail-index.h
index 8add21b748..a54c41d9f6 100644
--- a/src/lib-index/mail-index.h
+++ b/src/lib-index/mail-index.h
@@ -555,11 +555,17 @@ void mail_index_lookup_first(struct mail_index_view *view,
 /* Append a new record to index. */
 void mail_index_append(struct mail_index_transaction *t, uint32_t uid,
 		       uint32_t *seq_r);
-/* Assign UIDs for mails with uid=0 or uid<first_uid. All the assigned UIDs
-   are higher than the highest unassigned UID (i.e. it doesn't try to fill UID
-   gaps). Assumes that mailbox is locked in a way that UIDs can be safely
-   assigned. Returns UIDs for all assigned messages, in their sequence order
-   (so UIDs are not necessary ascending). */
+/* Assign new UIDs for mails with uid=0 or uid<min_allowed_uid. All the new
+   UIDs are >= first_new_uid, an also higher than the highest seen uid (i.e. it
+   doesn't try to fill UID gaps). Assumes that mailbox is locked in a way that
+   UIDs can be safely assigned. Returns UIDs for all assigned messages, in
+   their sequence order (so UIDs are not necessary ascending). */
+void mail_index_append_finish_uids_full(struct mail_index_transaction *t,
+					uint32_t min_allowed_uid,
+					uint32_t first_new_uid,
+					ARRAY_TYPE(seq_range) *uids_r);
+/* Call mail_index_append_finish_uids_full() with first_uid used for both
+   min_allowed_uid and first_new_uid. */
 void mail_index_append_finish_uids(struct mail_index_transaction *t,
 				   uint32_t first_uid,
 				   ARRAY_TYPE(seq_range) *uids_r);