diff --git a/test_regress/driver.pl b/test_regress/driver.pl
index 968b89f81..cbd9ba9ea 100755
--- a/test_regress/driver.pl
+++ b/test_regress/driver.pl
@@ -578,6 +578,7 @@ sub new {
         make_pli => 0,          # need to compile pli
         sc_time_resolution => "SC_PS",  # Keep - PS is SystemC default
         sim_time => 1100,
+        threads => -1,          # --threads (negative means auto based on scenario)
         benchmark => $opt_benchmark,
         verbose => $opt_verbose,
         run_env => '',
@@ -902,6 +903,7 @@ sub compile_vlt_flags {
                           @{$param{verilator_flags}},
                           @{$param{verilator_flags2}},
                           @{$param{verilator_flags3}});
+    die "%Error: specify threads via 'threads =>' argument, not as a command line option" unless ($checkflags !~ /(^|\s)-?-threads\s/ && $checkflags !~ /(^|\s)-?-no-threads($|\s)/);
     $self->{sc} = 1 if ($checkflags =~ /-sc\b/);
     $self->{trace} = ($opt_trace || $checkflags =~ /-trace\b/
                       || $checkflags =~ /-trace-fst\b/);
@@ -920,8 +922,7 @@ sub compile_vlt_flags {
     unshift @verilator_flags, "--rr" if $opt_rr;
     unshift @verilator_flags, "--x-assign unique";  # More likely to be buggy
     unshift @verilator_flags, "--trace" if $opt_trace;
-    my $threads = ::calc_threads($Vltmt_threads);
-    unshift @verilator_flags, "--threads $threads" if $param{vltmt} && $checkflags !~ /-threads /;
+    unshift @verilator_flags, "--threads $param{threads}" if $param{threads} >= 0;
     unshift @verilator_flags, "--trace-threads 2" if $param{vltmt} && $checkflags =~ /-trace-fst /;
     unshift @verilator_flags, "--debug-partition" if $param{vltmt};
     unshift @verilator_flags, "-CFLAGS -ggdb -LDFLAGS -ggdb" if $opt_gdbsim;
@@ -972,6 +973,9 @@ sub compile {
     return 1 if $self->errors || $self->skips || $self->unsupporteds;
     $self->oprint("Compile\n") if $self->{verbose};
 
+    die "%Error: 'threads =>' argument must be <= 1 for vlt scenario" if $param{vlt} && $param{threads} > 1;
+    $param{threads} = ::calc_threads($Vltmt_threads) if ($param{threads} < 0 && $param{vltmt});
+
     compile_vlt_cmd(%param);
 
     if (!$param{make_top_shell}) {
diff --git a/test_regress/t/t_depth_flop.pl b/test_regress/t/t_depth_flop.pl
index dabf3116e..8b4ad07ec 100755
--- a/test_regress/t/t_depth_flop.pl
+++ b/test_regress/t/t_depth_flop.pl
@@ -11,7 +11,8 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 scenarios(vltmt => 1);  # Note issue shows up with --threads
 
 compile(
-    verilator_flags2 => ['--compiler clang --threads 2 -Wno-UNOPTTHREADS'],
+    verilator_flags2 => ['--compiler clang -Wno-UNOPTTHREADS'],
+    threads => 2
     );
 
 ok(1);
diff --git a/test_regress/t/t_dotfiles.pl b/test_regress/t/t_dotfiles.pl
index 31b8ac837..a9b52715e 100755
--- a/test_regress/t/t_dotfiles.pl
+++ b/test_regress/t/t_dotfiles.pl
@@ -14,7 +14,8 @@ scenarios(vltmt => 1);
 top_filename("t/t_gen_alw.v");
 
 compile(
-    v_flags2 => ["--debug --debugi 5 --threads 2"]
+    v_flags2 => ["--debug --debugi 5"],
+    threads => 2
     );
 
 foreach my $dotname ("linkcells", "task_call", "gate_simp", "gate_opt",
diff --git a/test_regress/t/t_embed1.pl b/test_regress/t/t_embed1.pl
index a28adebe6..08e4c042c 100755
--- a/test_regress/t/t_embed1.pl
+++ b/test_regress/t/t_embed1.pl
@@ -22,6 +22,7 @@ mkdir $child_dir;
         (VM_PREFIX => "$Self->{VM_PREFIX}_child",
          top_filename => "$Self->{name}_child.v",
          verilator_flags => ["-cc", "-Mdir", "${child_dir}", "--debug-check"],
+         threads => $Self->{vltmt} ? $Self->get_default_vltmt_threads() : 0
         );
 
     run(logfile => "${child_dir}/vlt_compile.log",
diff --git a/test_regress/t/t_gantt.pl b/test_regress/t/t_gantt.pl
index c757d3fbe..1f92de577 100755
--- a/test_regress/t/t_gantt.pl
+++ b/test_regress/t/t_gantt.pl
@@ -18,8 +18,9 @@ scenarios(vlt_all => 1);
 top_filename("t/t_gen_alw.v");
 
 compile(
+    v_flags2 => ["--prof-exec"],
     # Checks below care about thread count, so use 2 (minimum reasonable)
-    v_flags2 => ["--prof-exec",  ($Self->{vltmt} ? "--threads 2" : "")]
+    threads => $Self->{vltmt} ? 2 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_hier_block.pl b/test_regress/t/t_hier_block.pl
index cffc7ba04..e861c733e 100755
--- a/test_regress/t/t_hier_block.pl
+++ b/test_regress/t/t_hier_block.pl
@@ -18,11 +18,12 @@ scenarios(vlt_all => 1);
 
 compile(
     v_flags2 => ['t/t_hier_block.cpp'],
-    verilator_flags2 => ['--stats', ($Self->{vltmt} ? ' --threads 6' : ''),
+    verilator_flags2 => ['--stats',
                          '--hierarchical',
                          '--Wno-TIMESCALEMOD',
                          '--CFLAGS', '"-pipe -DCPP_MACRO=cplusplus"'
     ],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_hier_block_nohier.pl b/test_regress/t/t_hier_block_nohier.pl
index 006c981b3..8da19e163 100755
--- a/test_regress/t/t_hier_block_nohier.pl
+++ b/test_regress/t/t_hier_block_nohier.pl
@@ -23,8 +23,8 @@ compile(
     v_flags2 => ['t/t_hier_block.cpp'],
     verilator_flags2 => ['--stats',
                          '+define+USE_VLT', 't/t_hier_block_vlt.vlt',
-                         '--CFLAGS', '"-pipe -DCPP_MACRO=cplusplus"',
-                         ($Self->{vltmt} ? ' --threads 6' : '')],
+                         '--CFLAGS', '"-pipe -DCPP_MACRO=cplusplus"'],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_hier_block_sc.pl b/test_regress/t/t_hier_block_sc.pl
index 139b280b9..8aff1358d 100755
--- a/test_regress/t/t_hier_block_sc.pl
+++ b/test_regress/t/t_hier_block_sc.pl
@@ -22,9 +22,9 @@ compile(
     verilator_flags2 => ['--sc',
                          '--stats',
                          '--hierarchical',
-                         ($Self->{vltmt} ? ' --threads 6' : ''),
                          '--CFLAGS', '"-pipe -DCPP_MACRO=cplusplus"'
     ],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_hier_block_sc_trace_fst.pl b/test_regress/t/t_hier_block_sc_trace_fst.pl
index 6c8dd260e..b2497ad14 100755
--- a/test_regress/t/t_hier_block_sc_trace_fst.pl
+++ b/test_regress/t/t_hier_block_sc_trace_fst.pl
@@ -22,11 +22,11 @@ compile(
     verilator_flags2 => ['--sc',
                          '--stats',
                          '--hierarchical',
-                         ($Self->{vltmt} ? ' --threads 6' : ''),
                          '--CFLAGS', '"-pipe -DCPP_MACRO=cplusplus"',
                          "--CFLAGS", '"-O0 -ggdb"',
                          "--trace-fst"
     ],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_hier_block_sc_trace_vcd.pl b/test_regress/t/t_hier_block_sc_trace_vcd.pl
index 3ce4b1da3..7239369c7 100755
--- a/test_regress/t/t_hier_block_sc_trace_vcd.pl
+++ b/test_regress/t/t_hier_block_sc_trace_vcd.pl
@@ -22,11 +22,11 @@ compile(
     verilator_flags2 => ['--sc',
                          '--stats',
                          '--hierarchical',
-                         ($Self->{vltmt} ? ' --threads 6' : ''),
                          '--CFLAGS', '"-pipe -DCPP_MACRO=cplusplus"',
                          "--CFLAGS", '"-O0 -ggdb"',
                          "--trace"
     ],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_hier_block_trace_fst.pl b/test_regress/t/t_hier_block_trace_fst.pl
index 29213f97b..753b9dda1 100755
--- a/test_regress/t/t_hier_block_trace_fst.pl
+++ b/test_regress/t/t_hier_block_trace_fst.pl
@@ -17,12 +17,12 @@ top_filename("t/t_hier_block.v");
 
 compile(
     v_flags2 => ['t/t_hier_block.cpp'],
-    verilator_flags2 => [($Self->{vltmt} ? ' --threads 6' : ''),
-                         '--hierarchical',
+    verilator_flags2 => ['--hierarchical',
                          '--Wno-TIMESCALEMOD',
                          '--trace-fst',
                          '--no-trace-underscore',  # To avoid handle mismatches
     ],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_hier_block_trace_vcd.pl b/test_regress/t/t_hier_block_trace_vcd.pl
index ed212b921..4f3b80f09 100755
--- a/test_regress/t/t_hier_block_trace_vcd.pl
+++ b/test_regress/t/t_hier_block_trace_vcd.pl
@@ -17,12 +17,12 @@ top_filename("t/t_hier_block.v");
 
 compile(
     v_flags2 => ['t/t_hier_block.cpp'],
-    verilator_flags2 => [($Self->{vltmt} ? ' --threads 6' : ''),
-                         '--hierarchical',
+    verilator_flags2 => ['--hierarchical',
                          '--Wno-TIMESCALEMOD',
                          '--trace',
                          '--no-trace-underscore',  # To avoid handle mismatches
     ],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_hier_block_vlt.pl b/test_regress/t/t_hier_block_vlt.pl
index 904182717..ef467ede9 100755
--- a/test_regress/t/t_hier_block_vlt.pl
+++ b/test_regress/t/t_hier_block_vlt.pl
@@ -22,8 +22,8 @@ compile(
                          '--hierarchical',
                          '+define+SHOW_TIMESCALE',
                          '+define+USE_VLT', 't/t_hier_block_vlt.vlt',
-                         '--CFLAGS', '"-pipe -DCPP_MACRO=cplusplus"',
-                         ($Self->{vltmt} ? ' --threads 6' : '')],
+                         '--CFLAGS', '"-pipe -DCPP_MACRO=cplusplus"'],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_inst_tree_inl0_pub1.pl b/test_regress/t/t_inst_tree_inl0_pub1.pl
index b06051080..bad6139b0 100755
--- a/test_regress/t/t_inst_tree_inl0_pub1.pl
+++ b/test_regress/t/t_inst_tree_inl0_pub1.pl
@@ -14,9 +14,9 @@ top_filename("t/t_inst_tree.v");
 
 my $default_vltmt_threads = $Self->get_default_vltmt_threads();
 compile(
-    verilator_flags2 => ['--stats', "$Self->{t_dir}/$Self->{name}.vlt",
-                         # Force 3 threads even if we have fewer cores
-                         $Self->{vltmt} ? "--threads $default_vltmt_threads" : ""]
+    verilator_flags2 => ['--stats', "$Self->{t_dir}/$Self->{name}.vlt"],
+    # Force 3 threads even if we have fewer cores
+    threads => $Self->{vltmt} ? $default_vltmt_threads : 0
     );
 
 sub checkRelativeRefs {
diff --git a/test_regress/t/t_lib_prot_shared.pl b/test_regress/t/t_lib_prot_shared.pl
index a770be51b..1a3f8af5f 100755
--- a/test_regress/t/t_lib_prot_shared.pl
+++ b/test_regress/t/t_lib_prot_shared.pl
@@ -56,10 +56,10 @@ while (1) {
 
     compile(
         verilator_flags2 => ["$secret_dir/secret.sv",
-                             ($Self->{vltmt} ? ' --threads 1' : ''),
                              "-LDFLAGS",
                              "'-Wl,-rpath,$abs_secret_dir -L$abs_secret_dir -l$secret_prefix'"],
         xsim_flags2 => ["$secret_dir/secret.sv"],
+        threads => $Self->{vltmt} ? 1 : 0
         );
 
     execute(
diff --git a/test_regress/t/t_pgo_profoutofdate_bad.pl b/test_regress/t/t_pgo_profoutofdate_bad.pl
index e2cfc96a1..3e78104a6 100755
--- a/test_regress/t/t_pgo_profoutofdate_bad.pl
+++ b/test_regress/t/t_pgo_profoutofdate_bad.pl
@@ -11,7 +11,7 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 scenarios(vltmt => 1);
 
 compile(
-    v_flags2 => ["--threads 2"],
+    threads => 2,
     fails => 1,
     expect_filename => $Self->{golden_filename},
     );
diff --git a/test_regress/t/t_pgo_threads.pl b/test_regress/t/t_pgo_threads.pl
index 24e300882..974bbe3c4 100755
--- a/test_regress/t/t_pgo_threads.pl
+++ b/test_regress/t/t_pgo_threads.pl
@@ -14,7 +14,8 @@ scenarios(vltmt => 1);
 top_filename("t/t_gen_alw.v");
 
 compile(
-    v_flags2 => ["--prof-pgo --threads 2"]
+    v_flags2 => ["--prof-pgo"],
+    threads => 2
     );
 
 execute(
@@ -30,8 +31,8 @@ file_grep("$Self->{obj_dir}/profile.vlt", qr/profile_data/i);
 compile(
     # Intentinally no --prof-pgo here to make sure profile data can be read in
     # without it (that is: --prof-pgo has no effect on profile_data hash names)
-    v_flags2 => ["--threads 2",
-                 " $Self->{obj_dir}/profile.vlt"],
+    v_flags2 => [" $Self->{obj_dir}/profile.vlt"],
+    threads => 2
     );
 
 execute(
diff --git a/test_regress/t/t_split_var_0.pl b/test_regress/t/t_split_var_0.pl
index 5f07afe64..0441871e4 100755
--- a/test_regress/t/t_split_var_0.pl
+++ b/test_regress/t/t_split_var_0.pl
@@ -14,8 +14,8 @@ scenarios(simulator => 1);
 # %Warning-UNOPTTHREADS: Thread scheduler is unable to provide requested parallelism; consider asking for fewer threads.
 # So use 6 threads here though it's not optimal in performace wise, but ok.
 compile(
-    verilator_flags2 => ['--stats' . ($Self->{vltmt} ? ' --threads 6' : ''),
-                         "$Self->{t_dir}/t_split_var_0.vlt"],
+    verilator_flags2 => ['--stats', "$Self->{t_dir}/t_split_var_0.vlt"],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_split_var_2_trace.pl b/test_regress/t/t_split_var_2_trace.pl
index c79ed778a..35d20007a 100755
--- a/test_regress/t/t_split_var_2_trace.pl
+++ b/test_regress/t/t_split_var_2_trace.pl
@@ -15,8 +15,8 @@ top_filename("t/t_split_var_0.v");
 # %Warning-UNOPTTHREADS: Thread scheduler is unable to provide requested parallelism; consider asking for fewer threads.
 # So use 6 threads here though it's not optimal in performace wise, but ok.
 compile(
-    verilator_flags2 => ['--cc --trace --stats' . ($Self->{vltmt} ? ' --threads 6' : ''),
-                         '+define+TEST_ATTRIBUTES'],
+    verilator_flags2 => ['--cc --trace --stats +define+TEST_ATTRIBUTES'],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_threads_counter_0.pl b/test_regress/t/t_threads_counter_0.pl
index 8ba463b4e..b93572929 100755
--- a/test_regress/t/t_threads_counter_0.pl
+++ b/test_regress/t/t_threads_counter_0.pl
@@ -13,7 +13,8 @@ scenarios(simulator => 1);
 top_filename("t/t_threads_counter.v");
 
 compile(
-    verilator_flags2 => ['--cc --no-threads'],
+    verilator_flags2 => ['--cc'],
+    threads => 0,
     );
 
 execute(
diff --git a/test_regress/t/t_threads_counter_1.pl b/test_regress/t/t_threads_counter_1.pl
index f1b1cf7b0..95a607bfd 100755
--- a/test_regress/t/t_threads_counter_1.pl
+++ b/test_regress/t/t_threads_counter_1.pl
@@ -13,7 +13,8 @@ scenarios(vltmt => 1);
 top_filename("t/t_threads_counter.v");
 
 compile(
-    verilator_flags2 => ['--cc --threads 1'],
+    verilator_flags2 => ['--cc'],
+    threads => 1
     );
 
 execute(
diff --git a/test_regress/t/t_threads_counter_2.pl b/test_regress/t/t_threads_counter_2.pl
index 460c79651..3625322fe 100755
--- a/test_regress/t/t_threads_counter_2.pl
+++ b/test_regress/t/t_threads_counter_2.pl
@@ -13,7 +13,8 @@ scenarios(vltmt => 1);
 top_filename("t/t_threads_counter.v");
 
 compile(
-    verilator_flags2 => ['--cc --threads 2'],
+    verilator_flags2 => ['--cc'],
+    threads => 2
     );
 
 execute(
diff --git a/test_regress/t/t_threads_counter_4.pl b/test_regress/t/t_threads_counter_4.pl
index 97ac33b97..20ed3feb9 100755
--- a/test_regress/t/t_threads_counter_4.pl
+++ b/test_regress/t/t_threads_counter_4.pl
@@ -13,7 +13,8 @@ scenarios(vltmt => 1);
 top_filename("t/t_threads_counter.v");
 
 compile(
-    verilator_flags2 => ['--cc --threads 4'],
+    verilator_flags2 => ['--cc'],
+    threads => 4
     );
 
 execute(
diff --git a/test_regress/t/t_threads_crazy.pl b/test_regress/t/t_threads_crazy.pl
index ee8031054..6bb21acb0 100755
--- a/test_regress/t/t_threads_crazy.pl
+++ b/test_regress/t/t_threads_crazy.pl
@@ -15,7 +15,8 @@ if ($Self->cfg_with_m32) {
 }
 
 compile(
-    verilator_flags2 => ['--cc --threads 1024'],
+    verilator_flags2 => ['--cc'],
+    threads => 1024
     );
 
 execute(
diff --git a/test_regress/t/t_threads_nondeterminism.pl b/test_regress/t/t_threads_nondeterminism.pl
index 418a03fc6..b584fa62d 100755
--- a/test_regress/t/t_threads_nondeterminism.pl
+++ b/test_regress/t/t_threads_nondeterminism.pl
@@ -13,7 +13,8 @@ scenarios(vltmt => 1);
 top_filename("t/t_threads_counter.v");
 
 compile(
-    verilator_flags2 => ['--cc --threads 2 --debug-nondeterminism --no-skip-identical'],
+    verilator_flags2 => ['--cc --debug-nondeterminism --no-skip-identical'],
+    threads => 2
     );
 
 execute(
diff --git a/test_regress/t/t_trace_litendian.pl b/test_regress/t/t_trace_litendian.pl
index 91cc2e48f..5b7289295 100755
--- a/test_regress/t/t_trace_litendian.pl
+++ b/test_regress/t/t_trace_litendian.pl
@@ -14,8 +14,8 @@ scenarios(simulator => 1);
 # %Warning-UNOPTTHREADS: Thread scheduler is unable to provide requested parallelism; consider asking for fewer threads.
 # Strangely, asking for more threads makes it go away.
 compile(
-    verilator_flags2 => ['--cc --trace --trace-params -Wno-LITENDIAN',
-                        ($Self->{vltmt} ? '--threads 6' : '')],
+    verilator_flags2 => ['--cc --trace --trace-params -Wno-LITENDIAN'],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_trace_litendian_fst.pl b/test_regress/t/t_trace_litendian_fst.pl
index 4918c10bf..3e24bf901 100755
--- a/test_regress/t/t_trace_litendian_fst.pl
+++ b/test_regress/t/t_trace_litendian_fst.pl
@@ -16,8 +16,8 @@ top_filename("t/t_trace_litendian.v");
 # %Warning-UNOPTTHREADS: Thread scheduler is unable to provide requested parallelism; consider asking for fewer threads.
 # Strangely, asking for more threads makes it go away.
 compile(
-    verilator_flags2 => ['--cc --trace-fst --trace-params -Wno-LITENDIAN',
-                        ($Self->{vltmt} ?  '--threads 6' : '')],
+    verilator_flags2 => ['--cc --trace-fst --trace-params -Wno-LITENDIAN'],
+    threads => $Self->{vltmt} ? 6 : 0
     );
 
 execute(
diff --git a/test_regress/t/t_trace_litendian_fst_sc.pl b/test_regress/t/t_trace_litendian_fst_sc.pl
index 56754b9df..b79e1e78f 100755
--- a/test_regress/t/t_trace_litendian_fst_sc.pl
+++ b/test_regress/t/t_trace_litendian_fst_sc.pl
@@ -20,8 +20,8 @@ else {
     # %Warning-UNOPTTHREADS: Thread scheduler is unable to provide requested parallelism; consider asking for fewer threads.
     # Strangely, asking for more threads makes it go away.
     compile(
-        verilator_flags2 => ['--sc --trace-fst --trace-params -Wno-LITENDIAN',
-                            ($Self->{vltmt} ?  '--threads 6' : '')],
+        verilator_flags2 => ['--sc --trace-fst --trace-params -Wno-LITENDIAN'],
+        threads => $Self->{vltmt} ? 6 : 0
         );
 
     execute(
diff --git a/test_regress/t/t_verilated_all.pl b/test_regress/t/t_verilated_all.pl
index 450b5bd9c..402f834d4 100755
--- a/test_regress/t/t_verilated_all.pl
+++ b/test_regress/t/t_verilated_all.pl
@@ -8,7 +8,7 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 # Version 2.0.
 # SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
 
-scenarios(vlt => 1);
+scenarios(vltmt => 1);
 
 my $root = "..";
 
@@ -17,10 +17,10 @@ compile(
     verilator_flags2 => ["--cc",
                          "--coverage-toggle --coverage-line --coverage-user",
                          "--trace --vpi ",
-                         "--threads 2",
                          "--trace-threads 1",
                          "--prof-exec", "--prof-pgo",
                          "$root/include/verilated_save.cpp"],
+    threads => 2
     );
 
 execute(
diff --git a/test_regress/t/t_verilated_threaded.pl b/test_regress/t/t_verilated_threaded.pl
index ec8edeb50..a11df1cfe 100755
--- a/test_regress/t/t_verilated_threaded.pl
+++ b/test_regress/t/t_verilated_threaded.pl
@@ -16,7 +16,8 @@ my $root = "..";
 
 compile(
     # Can't use --coverage and --savable together, so cheat and compile inline
-    verilator_flags2 => ["--cc --coverage-toggle --coverage-line --coverage-user --trace --threads 1 --vpi $root/include/verilated_save.cpp"],
+    verilator_flags2 => ["--cc --coverage-toggle --coverage-line --coverage-user --trace --vpi $root/include/verilated_save.cpp"],
+    threads => 1
     );
 
 execute(
diff --git a/test_regress/t/t_wrapper_context.pl b/test_regress/t/t_wrapper_context.pl
index e95e77250..30c3a78a3 100755
--- a/test_regress/t/t_wrapper_context.pl
+++ b/test_regress/t/t_wrapper_context.pl
@@ -14,8 +14,9 @@ compile(
     make_top_shell => 0,
     make_main => 0,
     # link threads library, add custom .cpp code, add tracing & coverage support
-    verilator_flags2 => ["-threads 1 --exe $Self->{t_dir}/$Self->{name}.cpp",
+    verilator_flags2 => ["--exe $Self->{t_dir}/$Self->{name}.cpp",
                          "--trace --coverage -cc"],
+    threads => 1,
     make_flags => 'CPPFLAGS_ADD=-DVL_NO_LEGACY',
     );
 
diff --git a/test_regress/t/t_wrapper_context_fst.pl b/test_regress/t/t_wrapper_context_fst.pl
index 8b40a7b2d..98b3ceb5a 100755
--- a/test_regress/t/t_wrapper_context_fst.pl
+++ b/test_regress/t/t_wrapper_context_fst.pl
@@ -16,8 +16,9 @@ compile(
     make_top_shell => 0,
     make_main => 0,
     # link threads library, add custom .cpp code, add tracing & coverage support
-    verilator_flags2 => ["-threads 1 --exe $Self->{t_dir}/t_wrapper_context.cpp",
+    verilator_flags2 => ["--exe $Self->{t_dir}/t_wrapper_context.cpp",
                          "--trace-fst --coverage -cc"],
+    threads => 1,
     make_flags => 'CPPFLAGS_ADD=-DVL_NO_LEGACY',
     );
 
diff --git a/test_regress/t/t_wrapper_context_seq.pl b/test_regress/t/t_wrapper_context_seq.pl
index 8ddf958f8..162a0c596 100755
--- a/test_regress/t/t_wrapper_context_seq.pl
+++ b/test_regress/t/t_wrapper_context_seq.pl
@@ -16,8 +16,9 @@ compile(
     make_top_shell => 0,
     make_main => 0,
     # link threads library, add custom .cpp code, add tracing & coverage support
-    verilator_flags2 => ["-threads 1 --exe $Self->{t_dir}/t_wrapper_context.cpp",
+    verilator_flags2 => ["--exe $Self->{t_dir}/t_wrapper_context.cpp",
                          "--trace --coverage -cc"],
+    threads => 1,
     make_flags => 'CPPFLAGS_ADD=-DVL_NO_LEGACY',
     );