diff --git a/ldap/servers/slapd/back-ldbm/ancestorid.c b/ldap/servers/slapd/back-ldbm/ancestorid.c
index 459a3df..6997732 100644
--- a/ldap/servers/slapd/back-ldbm/ancestorid.c
+++ b/ldap/servers/slapd/back-ldbm/ancestorid.c
@@ -80,7 +80,12 @@ static int ldbm_get_nonleaf_ids(backend *be, DB_TXN *txn, IDList **idl, ImportJo
         ret = dbc->c_get(dbc,&key,&data,DB_NEXT_NODUP);
         if ((ret == 0) && (*(char*)key.data == EQ_PREFIX)) {
             id = (ID) strtoul((char*)key.data+1, NULL, 10);
-            idl_insert(&nodes, id);
+            // TEL 20180711 - switch to idl_append instead of idl_insert because there is no
+            // no need to keep the list constantly sorted, which can be very expensive with
+            // large databases (exacerbated by the fact that the parentid btree ordering is
+            // lexical, but the idl_insert ordering is numeric).  It is enough to gather tham all
+            // together and sort them once at the end.
+            idl_append_extend(&nodes, id);
         }
         key_count++;
         if(!(key_count % PROGRESS_INTERVAL)){
@@ -104,6 +109,17 @@ static int ldbm_get_nonleaf_ids(backend *be, DB_TXN *txn, IDList **idl, ImportJo
     if (ret == DB_NOTFOUND) ret = 0;
     if (ret != 0) ldbm_nasty("ldbm_get_nonleaf_ids", sourcefile,13030,ret);
 
+    if (ret == 0) {
+        // now sort it
+        import_log_notice(job, SLAPI_LOG_INFO, "ldbm_get_nonleaf_ids",
+            "Starting sort of ancestorid non-leaf IDs.");
+
+        qsort((void *)&nodes->b_ids[0], nodes->b_nids, (size_t)sizeof(ID), idl_sort_cmp);
+
+        import_log_notice(job, SLAPI_LOG_INFO, "ldbm_get_nonleaf_ids",
+            "Finished sort of ancestorid non-leaf IDs.");
+    }
+
  out:
     /* Close the cursor */
     if (dbc != NULL) {