diff --git a/test_regress/t/t_mailbox.out b/test_regress/t/t_mailbox.out
index 4d5432212..d09756948 100644
--- a/test_regress/t/t_mailbox.out
+++ b/test_regress/t/t_mailbox.out
@@ -1,6 +1,6 @@
-%Error: t/t_mailbox.v:20:4: Can't find typedef: 'mailbox'
-   20 |    mailbox #(int) m;
+%Error: t/t_mailbox.v:24:4: Can't find typedef: 'mailbox'
+   24 |    mailbox #(int) m;
       |    ^~~~~~~
-%Error: Internal Error: t/t_mailbox.v:20:14: ../V3LinkDot.cpp:#: Pin not under instance?
-   20 |    mailbox #(int) m;
+%Error: Internal Error: t/t_mailbox.v:24:14: ../V3LinkDot.cpp:#: Pin not under instance?
+   24 |    mailbox #(int) m;
       |              ^~~
diff --git a/test_regress/t/t_mailbox.v b/test_regress/t/t_mailbox.v
index 1ef2bc5e2..64e2ba175 100644
--- a/test_regress/t/t_mailbox.v
+++ b/test_regress/t/t_mailbox.v
@@ -16,8 +16,12 @@
 //     function int try_peek( ref T message );
 //  endclass
 
+`ifndef MAILBOX_T
+ `define MAILBOX_T mailbox
+`endif
+
 module t(/*AUTOARG*/);
-   mailbox #(int) m;
+   `MAILBOX_T #(int) m;
    int     msg;
    int     out;
 
@@ -50,8 +54,8 @@ module t(/*AUTOARG*/);
       msg = 125;
       m.put(msg);
       m.put(msg);
-      m.try_put(msg);
-      m.try_put(msg);
+      if (m.try_put(msg) == 0) $stop;
+      if (m.try_put(msg) == 0) $stop;
       if (m.num() != 4) $stop;
       if (m.try_put(msg) != 0) $stop;
       if (m.num() != 4) $stop;
diff --git a/test_regress/t/t_mailbox_bad.out b/test_regress/t/t_mailbox_bad.out
index 4d5432212..218a34ad3 100644
--- a/test_regress/t/t_mailbox_bad.out
+++ b/test_regress/t/t_mailbox_bad.out
@@ -1,6 +1,6 @@
-%Error: t/t_mailbox.v:20:4: Can't find typedef: 'mailbox'
-   20 |    mailbox #(int) m;
+%Error: t/t_mailbox_bad.v:8:4: Can't find typedef: 'mailbox'
+    8 |    mailbox #(int) m;
       |    ^~~~~~~
-%Error: Internal Error: t/t_mailbox.v:20:14: ../V3LinkDot.cpp:#: Pin not under instance?
-   20 |    mailbox #(int) m;
+%Error: Internal Error: t/t_mailbox_bad.v:8:14: ../V3LinkDot.cpp:#: Pin not under instance?
+    8 |    mailbox #(int) m;
       |              ^~~
diff --git a/test_regress/t/t_mailbox_bad.pl b/test_regress/t/t_mailbox_bad.pl
index 8de551634..a083f46f5 100755
--- a/test_regress/t/t_mailbox_bad.pl
+++ b/test_regress/t/t_mailbox_bad.pl
@@ -10,10 +10,7 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 
 scenarios(vlt => 1);
 
-top_filename("t_mailbox.v");
-
 lint(
-    verilator_flags2 => ["--xml-only"],
     fails => 1,
     expect_filename => $Self->{golden_filename},
     );
diff --git a/test_regress/t/t_mailbox_class.out b/test_regress/t/t_mailbox_class.out
new file mode 100644
index 000000000..da24a9ec0
--- /dev/null
+++ b/test_regress/t/t_mailbox_class.out
@@ -0,0 +1,17 @@
+%Error-UNSUPPORTED: t/t_mailbox_class.v:21:25: Unsupported: event controls in methods
+                                             : ... In instance $unit::mailbox_cls
+   21 |       if (m_bound != 0) wait (m_q.size() < m_bound);
+      |                         ^~~~
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error-UNSUPPORTED: t/t_mailbox_class.v:35:7: Unsupported: event controls in methods
+                                            : ... In instance $unit::mailbox_cls
+   35 |       wait (m_q.size() != 0);
+      |       ^~~~
+%Error-UNSUPPORTED: t/t_mailbox_class.v:49:7: Unsupported: event controls in methods
+                                            : ... In instance $unit::mailbox_cls
+   49 |       wait (m_q.size() != 0);
+      |       ^~~~
+%Error-UNSUPPORTED: t/t_mailbox_class.v:21:31: Unsupported: Cannot detect changes on expression of complex type (see combinational cycles reported by UNOPTFLAT)
+   21 |       if (m_bound != 0) wait (m_q.size() < m_bound);
+      |                               ^~~
+%Error: Exiting due to
diff --git a/test_regress/t/t_mailbox_class.pl b/test_regress/t/t_mailbox_class.pl
new file mode 100755
index 000000000..830c5f044
--- /dev/null
+++ b/test_regress/t/t_mailbox_class.pl
@@ -0,0 +1,24 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2020 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(simulator => 1);
+
+compile(
+    verilator_flags2 => ["--timing"],
+    fails => $Self->{vlt_all},
+    expect_filename => $Self->{golden_filename},
+    );
+
+execute(
+    check_finished => 1,
+    ) if !$Self->{vlt_all};
+
+ok(1);
+1;
diff --git a/test_regress/t/t_mailbox_class.v b/test_regress/t/t_mailbox_class.v
new file mode 100644
index 000000000..31619225c
--- /dev/null
+++ b/test_regress/t/t_mailbox_class.v
@@ -0,0 +1,65 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2022 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+class mailbox_cls #(type T=int);
+   // Test an implementation similar to what Verilator will do internally
+   int m_bound;
+   T m_q[$];
+
+   function new(int bound = 0);
+      m_bound = bound;
+   endfunction
+
+   function int num();
+      return m_q.size();
+   endfunction
+
+   task put(T message);
+      if (m_bound != 0) wait (m_q.size() < m_bound);
+      m_q.push_back(message);
+   endtask
+   function int try_put(T message);
+      if (m_bound != 0 && m_q.size() < m_bound) begin
+         m_q.push_back(message);
+         return 1;
+      end
+      else begin
+         return 0;
+      end
+   endfunction
+
+   task get(ref T message);
+      wait (m_q.size() != 0);
+      message = m_q.pop_front();
+   endtask
+   function int try_get(ref T message);
+      if (m_q.size() != 0) begin
+         message = m_q.pop_front();
+         return 1;
+      end
+      else begin
+         return 0;
+      end
+   endfunction
+
+   task peek(ref T message);
+      wait (m_q.size() != 0);
+      message = m_q[0];
+   endtask
+   function int try_peek(ref T message);
+      if (m_q.size() != 0) begin
+         message = m_q[0];
+         return 1;
+      end
+      else begin
+         return 0;
+      end
+   endfunction
+endclass
+
+`define MAILBOX_T mailbox_cls
+
+`include "t_mailbox.v"
diff --git a/test_regress/t/t_semaphore.out b/test_regress/t/t_semaphore.out
index 76d60e04d..95ce89973 100644
--- a/test_regress/t/t_semaphore.out
+++ b/test_regress/t/t_semaphore.out
@@ -1,7 +1,7 @@
-%Error: t/t_semaphore.v:17:4: Can't find typedef: 'semaphore'
-   17 |    semaphore s;
+%Error: t/t_semaphore.v:21:4: Can't find typedef: 'semaphore'
+   21 |    semaphore s;
       |    ^~~~~~~~~
-%Error: t/t_semaphore.v:18:4: Can't find typedef: 'semaphore'
-   18 |    semaphore s2;
+%Error: t/t_semaphore.v:22:4: Can't find typedef: 'semaphore'
+   22 |    semaphore s2;
       |    ^~~~~~~~~
 %Error: Exiting due to
diff --git a/test_regress/t/t_semaphore.v b/test_regress/t/t_semaphore.v
index c191b2c13..500fac7e8 100644
--- a/test_regress/t/t_semaphore.v
+++ b/test_regress/t/t_semaphore.v
@@ -12,10 +12,14 @@
 //     function int try_get(int keyCount = 1);
 //  endclass
 
+`ifndef SEMAPHORE_T
+ `define SEMAPHORE_T semaphore
+`endif
+
 module t(/*AUTOARG*/);
    // From UVM:
-   semaphore s;
-   semaphore s2;
+   `SEMAPHORE_T s;
+   `SEMAPHORE_T s2;
    int       msg;
 
    initial begin
@@ -23,7 +27,7 @@ module t(/*AUTOARG*/);
       if (s.try_get() == 0) $stop;
       if (s.try_get() != 0) $stop;
 
-      s = new(0);
+      s = new;
       if (s.try_get() != 0) $stop;
 
       s.put();
diff --git a/test_regress/t/t_semaphore_bad.out b/test_regress/t/t_semaphore_bad.out
index 76d60e04d..c07616459 100644
--- a/test_regress/t/t_semaphore_bad.out
+++ b/test_regress/t/t_semaphore_bad.out
@@ -1,7 +1,4 @@
-%Error: t/t_semaphore.v:17:4: Can't find typedef: 'semaphore'
-   17 |    semaphore s;
-      |    ^~~~~~~~~
-%Error: t/t_semaphore.v:18:4: Can't find typedef: 'semaphore'
-   18 |    semaphore s2;
+%Error: t/t_semaphore_bad.v:8:4: Can't find typedef: 'semaphore'
+    8 |    semaphore s;
       |    ^~~~~~~~~
 %Error: Exiting due to
diff --git a/test_regress/t/t_semaphore_bad.pl b/test_regress/t/t_semaphore_bad.pl
index 92483cce2..a083f46f5 100755
--- a/test_regress/t/t_semaphore_bad.pl
+++ b/test_regress/t/t_semaphore_bad.pl
@@ -10,10 +10,7 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 
 scenarios(vlt => 1);
 
-top_filename("t_semaphore.v");
-
 lint(
-    verilator_flags2 => ["--xml-only"],
     fails => 1,
     expect_filename => $Self->{golden_filename},
     );
diff --git a/test_regress/t/t_semaphore_class.out b/test_regress/t/t_semaphore_class.out
new file mode 100644
index 000000000..54be71860
--- /dev/null
+++ b/test_regress/t/t_semaphore_class.out
@@ -0,0 +1,6 @@
+%Error-UNSUPPORTED: t/t_semaphore_class.v:17:7: Unsupported: event controls in methods
+                                              : ... In instance $unit::semaphore_cls
+   17 |       wait (m_keys >= keyCount);
+      |       ^~~~
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error: Exiting due to
diff --git a/test_regress/t/t_semaphore_class.pl b/test_regress/t/t_semaphore_class.pl
new file mode 100755
index 000000000..830c5f044
--- /dev/null
+++ b/test_regress/t/t_semaphore_class.pl
@@ -0,0 +1,24 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2020 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(simulator => 1);
+
+compile(
+    verilator_flags2 => ["--timing"],
+    fails => $Self->{vlt_all},
+    expect_filename => $Self->{golden_filename},
+    );
+
+execute(
+    check_finished => 1,
+    ) if !$Self->{vlt_all};
+
+ok(1);
+1;
diff --git a/test_regress/t/t_semaphore_class.v b/test_regress/t/t_semaphore_class.v
new file mode 100644
index 000000000..9460c6cf4
--- /dev/null
+++ b/test_regress/t/t_semaphore_class.v
@@ -0,0 +1,33 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2022 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+class semaphore_cls;
+   // Test an implementation similar to what Verilator will do internally
+   int m_keys;
+   function new(int keyCount = 0);
+      m_keys = keyCount;
+   endfunction
+   function void put(int keyCount = 1);
+      m_keys += keyCount;
+   endfunction
+   task get(int keyCount = 1);
+      wait (m_keys >= keyCount);
+      m_keys -= keyCount;
+   endtask
+   function int try_get(int keyCount = 1);
+      if (m_keys >= keyCount) begin
+         m_keys -= keyCount;
+         return 1;
+      end
+      else begin
+         return 0;
+      end
+   endfunction
+endclass
+
+`define SEMAPHORE_T semaphore_cls
+
+`include "t_semaphore.v"