diff --git a/test_regress/t/t_const_opt_red.pl b/test_regress/t/t_const_opt_red.pl
index b46d46042..b8d7ae067 100755
--- a/test_regress/t/t_const_opt_red.pl
+++ b/test_regress/t/t_const_opt_red.pl
@@ -11,6 +11,7 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 scenarios(simulator => 1);
 
 compile(
+    verilator_flags2=>["-Wno-UNOPTTHREADS"],
     );
 
 execute(