diff --git a/test_regress/t/t_event_control_assign.pl b/test_regress/t/t_event_control_assign.pl
index 00a80e5f2a4..06ac175ad21 100755
--- a/test_regress/t/t_event_control_assign.pl
+++ b/test_regress/t/t_event_control_assign.pl
@@ -13,6 +13,8 @@
 compile(
     verilator_flags2 => ["--exe --main --timing"],
     make_main => 0,
+    # Multithreading would cause a warning on event assignments
+    threads => 1,
     );
 
 execute(
diff --git a/test_regress/t/t_event_copy.pl b/test_regress/t/t_event_copy.pl
index be66c40e690..bce8f74ca85 100755
--- a/test_regress/t/t_event_copy.pl
+++ b/test_regress/t/t_event_copy.pl
@@ -13,6 +13,7 @@
 compile(
     fails => $Self->{vlt_all},
     expect_filename => $Self->{golden_filename},
+    threads => 1,
     );
 
 execute(