diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index c634c3c2e0..60a2cc13f1 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -1801,6 +1801,9 @@ func SetEthConfig(ctx *cli.Context, stack *node.Node, cfg *ethconfig.Config) {
 		if ctx.IsSet(DataDirFlag.Name) {
 			chaindb := tryMakeReadOnlyDatabase(ctx, stack)
 			if rawdb.ReadCanonicalHash(chaindb, 0) != (common.Hash{}) {
+				// signal fallback to preexisting chain on disk
+				cfg.Genesis = nil
+
 				genesis, err := core.ReadGenesis(chaindb)
 				if err != nil {
 					Fatalf("Could not read genesis from database: %v", err)