--- ./lib/backend/dbi.c.orig	2020-11-18 09:37:08.314743771 +0000
+++ ./lib/backend/dbi.c	2020-11-18 09:42:34.025792074 +0000
@@ -77,7 +77,7 @@ dbDetectBackend(rpmdb rdb)
 	}
     }
 
-    if (!cfg) {
+    if (!cfg && (rdb->db_flags & RPMDB_FLAG_REBUILD) != 0) {
 	rpmlog(RPMLOG_WARNING, _("invalid %%_db_backend: %s\n"), db_backend);
 	goto exit;
     }
@@ -97,7 +97,7 @@ dbDetectBackend(rpmdb rdb)
 		rpmlog(RPMLOG_WARNING,
 			_("Converting database from %s to %s backend\n"),
 			ondisk->name, cfg->name);
-	    } else {
+	    } else if (*db_backend) {
 		rpmlog(RPMLOG_WARNING,
 		    _("Found %s %s database while attempting %s backend: "
 		    "using %s backend.\n"),