diff --git a/go/cmd/vtcombo/cli/main.go b/go/cmd/vtcombo/cli/main.go
index 72dcd3fa8b9..7b9143f1384 100644
--- a/go/cmd/vtcombo/cli/main.go
+++ b/go/cmd/vtcombo/cli/main.go
@@ -178,7 +178,7 @@ func run(cmd *cobra.Command, args []string) (err error) {
 
 	// vtctld UI requires the cell flag
 	cmd.Flags().Set("cell", tpb.Cells[0])
-	if cmd.Flags().Lookup("log_dir") == nil {
+	if f := cmd.Flags().Lookup("log_dir"); f != nil && !f.Changed {
 		cmd.Flags().Set("log_dir", "$VTDATAROOT/tmp")
 	}