diff --git a/Changes b/Changes
index 78c5b3c5d..e428484f5 100644
--- a/Changes
+++ b/Changes
@@ -7,6 +7,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 ***  Add --trace-depth option for minimizing VCD file size. [Emerson Suguimoto]
 
+***  With VL_DEBUG, show wires causing convergance errors. [Mike Shinkarovsky]
+
 **** Fix isolate_assignments when many signals per always. [Mike Shinkarovsky]
 
 **** Fix isolate_assignments across task/func temporaries. [Mike Shinkarovsky]
diff --git a/bin/verilator b/bin/verilator
index 03a8cd2a2..3855f1aa1 100755
--- a/bin/verilator
+++ b/bin/verilator
@@ -1635,12 +1635,18 @@ For example:
    always @ (b)  a=b
 
 will toggle forever and thus the executable will give the didn't converge
-error to prevent an infinite loop.  To debug this, compile the Verilated
-.cpp files with -DVL_DEBUG, then call Verilated::debug(1) in your main.cpp.
-This will cause each module to print a message when it's invoked.  From
-that it should be obvious what routine(s) are part of the infinite loop.
-Then in Gdb, add a break point at the routine entry point and "print *this"
-on each loop so you can see what variables are changing each invocation.
+error to prevent an infinite loop.
+
+To debug this, run Verilator with --profile-cfuncs.  Run make on the
+generated files with "CPPFLAGS_ADD=-DVL_DEBUG". Then call
+Verilated::debug(1) in your main.cpp.
+
+This will cause each change in a variable to print a message.  Near the
+bottom you'll see the code and variable that causes the problem.  For the
+program above:
+
+        CHANGE: filename.v:1: b
+        CHANGE: filename.v:2: a
 
 =back
 
diff --git a/src/V3EmitC.cpp b/src/V3EmitC.cpp
index bb1b8b7a8..b65ce1bdb 100644
--- a/src/V3EmitC.cpp
+++ b/src/V3EmitC.cpp
@@ -687,6 +687,21 @@ class EmitCImp : EmitCStmts {
 	if (gotOne) {
 	    puts(");\n");
 	    //puts("VL_DEBUG_IF( if (__req) cout<<\"\tCLOCKREQ );");
+	    for (vector<AstChangeDet*>::iterator it = m_blkChangeDetVec.begin();
+		 it != m_blkChangeDetVec.end(); ++it) {
+		AstChangeDet* nodep = *it;
+		if (nodep->lhsp()) {
+		    puts("VL_DEBUG_IF( if(__req && (");
+		    bool gotOneIgnore = false;
+		    doubleOrDetect(nodep, gotOneIgnore);
+		    string varname;
+		    if (nodep->lhsp()->castVarRef()) {
+			varname = ": "+nodep->lhsp()->castVarRef()->varp()->prettyName();
+		    }
+		    puts(")) cout<<\"\tCHANGE: "+nodep->fileline()->ascii()
+			 +varname+"\"<<endl; );");
+		}
+	    }
 	}
     }
 
diff --git a/src/V3Gate.cpp b/src/V3Gate.cpp
index 750eece36..5ca963cd3 100644
--- a/src/V3Gate.cpp
+++ b/src/V3Gate.cpp
@@ -198,10 +198,18 @@ public:
 	m_substTreep = NULL;
 	m_buffersOnly = buffersOnly;
 	m_lhsVarRef = NULL;
+	// Iterate
 	nodep->accept(*this);
+	// Check results
 	if (!m_substTreep) {
 	    clearSimple("No assignment found\n");
 	}
+	for (GateVarRefList::const_iterator it = rhsVarRefs().begin();
+	     it != rhsVarRefs().end(); ++it) {
+	    if (m_lhsVarRef && m_lhsVarRef->varScopep() == (*it)->varScopep()) {
+		clearSimple("Circular logic\n");  // Oh my, we'll get a UNOPTFLAT much later.
+	    }
+	}
 	if (debug()>=9 && !m_isSimple) {
 	    nodep->dumpTree(cout,"\tgate!Ok: ");
 	}
@@ -224,6 +232,7 @@ private:
     //Entire netlist:
     // AstVarScope::userp	-> GateVarVertex* for usage var, 0=not set yet
     // {statement}Node::userp	-> GateLogicVertex* for this statement
+
     // STATE
     V3Graph		m_graph;	// Scoreboard of var usages/dependencies
     GateLogicVertex*	m_logicVertexp;	// Current statement being tracked, NULL=ignored
@@ -458,6 +467,7 @@ void GateVisitor::optimizeSignals(bool allowMultiIn) {
 			    }
 			}
 		    }
+		    // Process it
 		    if (!doit) {
 			if (allowMultiIn && (debug()>=9)) {
 			    UINFO(9, "Not ok simp"<<okVisitor.isSimple()<<" mi"<<multiInputs
diff --git a/test_regress/driver.pl b/test_regress/driver.pl
index 7ba1b4814..6049a96d4 100755
--- a/test_regress/driver.pl
+++ b/test_regress/driver.pl
@@ -206,6 +206,7 @@ sub new {
 	'v3' => 0,
 	verilator_flags => [split(/\s+/,"-cc")],
 	verilator_make_gcc => 1,
+	verilated_debug => $Opt_Verilated_Debug,
 	stdout_filename => undef,	# Redirect stdout
 	@_};
     bless $self, $class;
@@ -545,7 +546,7 @@ sub _make_main {
 	print $fh "int main(int argc, char **argv, char **env) {\n";
 	print $fh "    double sim_time = 1000;\n";
     }
-    print $fh "    Verilated::debug(".($Opt_Verilated_Debug?1:0).");\n";
+    print $fh "    Verilated::debug(".($self->{verilated_debug}?1:0).");\n";
     print $fh "    topp = new $VM_PREFIX (\"TOP\");\n";
     my $set;
     if ($self->sp) {
diff --git a/test_regress/t/t_unopt_converge.v b/test_regress/t/t_unopt_converge.v
new file mode 100644
index 000000000..ed827962f
--- /dev/null
+++ b/test_regress/t/t_unopt_converge.v
@@ -0,0 +1,26 @@
+// $Id$
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2007 by Wilson Snyder.
+
+module t (/*AUTOARG*/
+   // Outputs
+   x,
+   // Inputs
+   clk
+   );
+
+`ifdef ALLOW_UNOPT
+   /*verilator lint_off UNOPTFLAT*/
+`endif
+
+   input clk;
+   output x;   // Avoid eliminating x
+
+   reg x;
+   always @* begin
+      x = ~x;
+   end
+
+endmodule
diff --git a/test_regress/t/t_unopt_converge_print_bad.pl b/test_regress/t/t_unopt_converge_print_bad.pl
new file mode 100755
index 000000000..e6aaba8f9
--- /dev/null
+++ b/test_regress/t/t_unopt_converge_print_bad.pl
@@ -0,0 +1,24 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("./driver.pl", @ARGV, $0); die; }
+# $Id$
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2007 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# General Public License or the Perl Artistic License.
+
+top_filename("t/t_unopt_converge.v");
+#$Last_Self->{verilated_debug} = 1;
+
+compile (
+	 v_flags2 => ['+define+ALLOW_UNOPT'],
+	 make_flags => 'CPPFLAGS_ADD=-DVL_DEBUG',
+	 );
+
+execute (
+	 fails=>1,
+	 expect=> '%Error: \S+:\d+: Verilated model didn\'t converge',
+     ) if $Last_Self->{v3};
+
+ok(1);
+1;
diff --git a/test_regress/t/t_unopt_converge_run_bad.pl b/test_regress/t/t_unopt_converge_run_bad.pl
new file mode 100755
index 000000000..477b101a9
--- /dev/null
+++ b/test_regress/t/t_unopt_converge_run_bad.pl
@@ -0,0 +1,22 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("./driver.pl", @ARGV, $0); die; }
+# $Id$
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2007 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# General Public License or the Perl Artistic License.
+
+top_filename("t/t_unopt_converge.v");
+
+compile (
+	 v_flags2 => ['+define+ALLOW_UNOPT'],
+	 );
+
+execute (
+	 fails=>1,
+	 expect=> '%Error: \S+:\d+: Verilated model didn\'t converge',
+     ) if $Last_Self->{v3};
+
+ok(1);
+1;
diff --git a/test_regress/t/t_unopt_converge_unopt_bad.pl b/test_regress/t/t_unopt_converge_unopt_bad.pl
new file mode 100755
index 000000000..45f504971
--- /dev/null
+++ b/test_regress/t/t_unopt_converge_unopt_bad.pl
@@ -0,0 +1,20 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("./driver.pl", @ARGV, $0); die; }
+# $Id$
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2007 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# General Public License or the Perl Artistic License.
+
+top_filename("t/t_unopt_converge.v");
+
+compile (
+	 fails=>1,
+	 expect=> '%Warning-UNOPT: t/t_unopt_converge.v:\d+: Signal unoptimizable: Feedback to public clock or circular logic: TOP->x
+.*
+%Error: Exiting due to '
+     ) if $Last_Self->{v3};
+
+ok(1);
+1;