diff --git a/src/V3Error.h b/src/V3Error.h
index f03506c62..d6b3720b1 100644
--- a/src/V3Error.h
+++ b/src/V3Error.h
@@ -97,6 +97,7 @@ public:
 	UNDRIVEN,	// No drivers
 	UNOPT,		// Unoptimizable block
 	UNOPTFLAT,	// Unoptimizable block after flattening
+        UNOPTTHREADS,   // Thread partitioner unable to fill all requested threads
 	UNPACKED,	// Unsupported unpacked
 	UNSIGNED,	// Comparison is constant due to unsigned arithmetic
 	UNUSED,		// No receivers
@@ -139,7 +140,8 @@ public:
 	    "PINMISSING", "PINNOCONNECT", "PINCONNECTEMPTY",
 	    "REALCVT", "REDEFMACRO",
 	    "SELRANGE", "STMTDLY", "SYMRSVDWORD", "SYNCASYNCNET",
-	    "UNDRIVEN", "UNOPT", "UNOPTFLAT", "UNPACKED", "UNSIGNED", "UNUSED",
+            "UNDRIVEN", "UNOPT", "UNOPTFLAT", "UNOPTTHREADS",
+            "UNPACKED", "UNSIGNED", "UNUSED",
 	    "USERERROR", "USERFATAL", "USERINFO", "USERWARN",
 	    "VARHIDDEN", "WIDTH", "WIDTHCONCAT",
 	    " MAX"
diff --git a/test_regress/t/t_bench_synmul.pl b/test_regress/t/t_bench_synmul.pl
index 3073a4cf7..3380cfefa 100755
--- a/test_regress/t/t_bench_synmul.pl
+++ b/test_regress/t/t_bench_synmul.pl
@@ -17,7 +17,9 @@ $Self->{cycles} = 100 if $Self->{cycles}<100;
 $Self->{sim_time} = $Self->{cycles}*100;
 
 compile(
-    v_flags2 => ["+define+SIM_CYCLES=$Self->{cycles} --stats"],
+    v_flags2 => ["+define+SIM_CYCLES=$Self->{cycles}",
+                 "--stats",
+                 "-Wno-UNOPTTHREADS"],
     );
 
 execute(
diff --git a/test_regress/t/t_emit_memb_limit.pl b/test_regress/t/t_emit_memb_limit.pl
index 713d6af9e..619a0cbc9 100755
--- a/test_regress/t/t_emit_memb_limit.pl
+++ b/test_regress/t/t_emit_memb_limit.pl
@@ -41,7 +41,9 @@ top_filename("$Self->{obj_dir}/t_emit_memb_limit.v");
 gen($Self->{top_filename}, 6000);
 
 compile(
-    verilator_flags2=>["-x-assign fast --x-initial fast"],
+    verilator_flags2=>["-x-assign fast --x-initial fast",
+                       "-Wno-UNOPTTHREADS",
+    ],
     );
 
 execute(
diff --git a/test_regress/t/t_gate_chained.pl b/test_regress/t/t_gate_chained.pl
index f77d4afd1..d5c61a969 100755
--- a/test_regress/t/t_gate_chained.pl
+++ b/test_regress/t/t_gate_chained.pl
@@ -44,7 +44,8 @@ top_filename("$Self->{obj_dir}/t_gate_chained.v");
 gen($Self->{top_filename});
 
 compile(
-    verilator_flags2=>["--stats --x-assign fast --x-initial fast"],
+    verilator_flags2=>["--stats --x-assign fast --x-initial fast",
+                       "-Wno-UNOPTTHREADS"],
     );
 
 execute(
diff --git a/test_regress/t/t_gate_tree.pl b/test_regress/t/t_gate_tree.pl
index 6abeb224b..78ab1582b 100755
--- a/test_regress/t/t_gate_tree.pl
+++ b/test_regress/t/t_gate_tree.pl
@@ -112,7 +112,8 @@ gen($Self->{top_filename});
 
 compile(
     v_flags2 => ["+define+SIM_CYCLES=$Self->{cycles}",],
-    verilator_flags2=>["--stats --x-assign fast --x-initial fast"],
+    verilator_flags2=>["--stats --x-assign fast --x-initial fast",
+                       "-Wno-UNOPTTHREADS"],
     );
 
 execute(
diff --git a/test_regress/t/t_math_synmul.pl b/test_regress/t/t_math_synmul.pl
index 89a4e77d9..a256a52dd 100755
--- a/test_regress/t/t_math_synmul.pl
+++ b/test_regress/t/t_math_synmul.pl
@@ -10,6 +10,7 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 scenarios(simulator => 1);
 
 compile(
+    verilator_flags2 => ["-Wno-UNOPTTHREADS"],
     );
 
 execute(