diff --git a/bin/verilator b/bin/verilator
index 696f7ff82..ec24d9502 100755
--- a/bin/verilator
+++ b/bin/verilator
@@ -3847,6 +3847,43 @@ as an unpacked struct or a large unpacked array. This typically occurs when
 
 The solution is to break the loop, as described for UNOPTFLAT.
 
+=item DIDNOTCONVERGE
+
+Error at runtime when model did not properly settle.
+
+Verilator sometimes has to evaluate combinatorial logic multiple times,
+usually around code where a UNOPTFLAT warning was issued, but disabled.
+For example:
+
+   always_comb b = ~a;
+   always_comb a = b
+
+This code will toggle forever, and thus to prevent an infinite loop, the
+executable will give the didn't converge error.
+
+To debug this, first is to review any UNOPTFLAT warnings that were ignored.
+Though typically it is safe to ignore UNOPTFLAT (at a performance cost), at
+the time of issuing a UNOPTFLAT Verilator didn't know if they would
+eventually converge and assumed the would.
+
+Next, run Verilator with --prof-cfuncs.  Run make on the generated files
+with "CPP_FLAGS=-DVL_DEBUG", to allow enabling runtime debug messages.
+Rerun the test.  Now just before the convergence error you should see
+additional output similar to this:
+
+   CHANGE: filename.v:1: b
+   CHANGE: filename.v:2: a
+
+This means that signal b and signal a keep changing, inspect the code that
+modifies these signals.  Note if many signals are getting printed then most
+likely all of them are oscillating.  It may also be that e.g. "a" may be
+oscillating, then "a" feeds signal "c" which then is also reported as
+oscillating.
+
+Finally, rare, more difficult cases can be debugged like a "C" program;
+either enter GDB and use its tracing facilities, or edit the generated C++
+code to add appropriate prints to see what is going on.
+
 =item ENDLABEL
 
 Warns that a label attached to a "end"-something statement does not match
@@ -4378,42 +4415,6 @@ warnings or errors, submit a bug report.
 This error indicates that you are using a Verilog language construct
 that is not yet supported in Verilator.  See the Limitations chapter.
 
-=item Verilated model didn't converge
-
-Verilator sometimes has to evaluate combinatorial logic multiple times,
-usually around code where a UNOPTFLAT warning was issued, but disabled.
-For example:
-
-   always @ (a)  b=~a;
-   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, first is to review any UNOPTFLAT warnings that were ignored,
-though typically these can be ignored (at a performance cost), convergence
-issues can also be flagged with this warning as Verilator didn't know if
-they would eventually converge.
-
-Next, run Verilator with --prof-cfuncs.  Run make on the generated
-files with "OPT=-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 variables that causes the problem.  For the program
-above:
-
-        CHANGE: filename.v:1: b
-        CHANGE: filename.v:2: a
-
-If many signals are getting printed then most likely each are oscillating
-(or there is a bug). It may also be that e.g. "a" may be oscillating, then
-"a" feeds signal "c" which then is also reported as oscillating.
-
-Finally, rare more difficult cases can be debugged like a "C" program;
-either enter GDB and use its tracing facilities, or edit the generated C++
-code to add appropriate prints to see what is going on.
-
 =back
 
 
diff --git a/include/verilated.cpp b/include/verilated.cpp
index b4e2097c2..f6de2b26b 100644
--- a/include/verilated.cpp
+++ b/include/verilated.cpp
@@ -1785,7 +1785,8 @@ void Verilated::debug(int level) VL_MT_SAFE {
                                 " Message prefix indicates {<thread>,<sequence_number>}.\n"););
 #else
         VL_PRINTF_MT("- Verilated::debug attempted,"
-                     " but compiled without VL_DEBUG, so messages suppressed.\n");
+                     " but compiled without VL_DEBUG, so messages suppressed.\n"
+                     "- Suggest remake using 'make ... CPPFLAGS=-DVL_DEBUG'\n");
 #endif
     }
 }
diff --git a/src/V3EmitC.cpp b/src/V3EmitC.cpp
index abe27d15f..34a6d5874 100644
--- a/src/V3EmitC.cpp
+++ b/src/V3EmitC.cpp
@@ -1196,7 +1196,7 @@ class EmitCImp : EmitCStmts {
                     puts(")) VL_DBG_MSGF(\"        CHANGE: ");
                     puts(protect(nodep->fileline()->filename()));
                     puts(":"+cvtToStr(nodep->fileline()->lineno()));
-                    puts(": "+varname+"\\n\"); );\n");
+                    puts(varname+"\\n\"); );\n");
                 }
             }
         }
@@ -2056,7 +2056,7 @@ void EmitCImp::emitStaticDecl(AstNodeModule* modp) {
 
 void EmitCImp::emitTextSection(AstType type) {
     int last_line = -999;
-    for (AstNode* nodep = m_modp->stmtsp(); nodep != NULL; nodep = nodep->nextp()) {
+    for (AstNode* nodep = m_modp->stmtsp(); nodep; nodep = nodep->nextp()) {
         if (const AstNodeText* textp = VN_CAST(nodep, NodeText)) {
             if (nodep->type() == type) {
                 if (last_line != nodep->fileline()->lineno()) {
@@ -2131,7 +2131,7 @@ void EmitCImp::emitSettleLoop(const std::string& eval_call, bool initial) {
     puts("int __VclockLoop = 0;\n");
     puts("QData __Vchange = 1;\n");
     puts("do {\n");
-    puts(    eval_call + "\n");
+    puts(    eval_call+"\n");
     puts(    "if (VL_UNLIKELY(++__VclockLoop > "+cvtToStr(v3Global.opt.convergeLimit())
              +")) {\n");
     puts(        "// About to fail, so enable debug to see what's not settling.\n");
@@ -2140,9 +2140,15 @@ void EmitCImp::emitSettleLoop(const std::string& eval_call, bool initial) {
     puts(        "Verilated::debug(1);\n");
     puts(        "__Vchange = "+protect("_change_request")+"(vlSymsp);\n");
     puts(        "Verilated::debug(__Vsaved_debug);\n");
-    puts(        "VL_FATAL_MT(__FILE__, __LINE__, __FILE__, \"Verilated model didn't ");
+    puts(        "VL_FATAL_MT(");
+    putsQuoted(protect(m_modp->fileline()->filename()));
+    puts(", ");
+    puts(cvtToStr(m_modp->fileline()->lineno()));
+    puts(", \"\",\n");
+    puts("\"Verilated model didn't ");
     if (initial) puts("DC ");
-    puts(        "converge\");\n");
+    puts("converge\\n\"\n");
+    puts("\"- See DIDNOTCONVERGE in the Verilator manual\");\n");
     puts(    "} else {\n");
     puts(        "__Vchange = "+protect("_change_request")+"(vlSymsp);\n");
     puts(    "}\n");
diff --git a/test_regress/driver.pl b/test_regress/driver.pl
index 1f3094748..dcc44f5cc 100755
--- a/test_regress/driver.pl
+++ b/test_regress/driver.pl
@@ -1960,6 +1960,7 @@ sub files_identical {
             } @l1;
             @l1 = map {
                 s/(Internal Error: [^\n]+\.cpp):[0-9]+:/$1:#:/;
+                s/^-V\{t[0-9]+,[0-9]+\}/-V{t#,#}/;  # --vlt vs --vltmt run differences
                 $_;
             } @l1;
             for (my $l=0; $l<=$#l1; ++$l) {
diff --git a/test_regress/t/t_unopt_converge_initial_run_bad.out b/test_regress/t/t_unopt_converge_initial_run_bad.out
new file mode 100644
index 000000000..3c8924f4f
--- /dev/null
+++ b/test_regress/t/t_unopt_converge_initial_run_bad.out
@@ -0,0 +1,5 @@
+-V{t#,#}- Verilated::debug is on. Message prefix indicates {<thread>,<sequence_number>}.
+-V{t#,#}+    Vt_unopt_converge_initial_run_bad::_change_request
+-V{t#,#}        CHANGE: t/t_unopt_converge_initial.v:18: x
+%Error: t/t_unopt_converge_initial.v:6: Verilated model didn't DC converge
+Aborting...
diff --git a/test_regress/t/t_unopt_converge_initial_run_bad.pl b/test_regress/t/t_unopt_converge_initial_run_bad.pl
index 5a8ed7eb0..b680fe33d 100755
--- a/test_regress/t/t_unopt_converge_initial_run_bad.pl
+++ b/test_regress/t/t_unopt_converge_initial_run_bad.pl
@@ -17,7 +17,7 @@ compile(
 
 execute(
     fails => 1,
-    expect => '%Error: \S+:\d+: Verilated model didn\'t DC converge',
+    expect_filename => $Self->{golden_filename},
     ) if $Self->{vlt_all};
 
 ok(1);
diff --git a/test_regress/t/t_unopt_converge_ndbg_bad.out b/test_regress/t/t_unopt_converge_ndbg_bad.out
new file mode 100644
index 000000000..1484d8577
--- /dev/null
+++ b/test_regress/t/t_unopt_converge_ndbg_bad.out
@@ -0,0 +1,2 @@
+%Error: t/t_unopt_converge.v:6: Verilated model didn't converge
+Aborting...
diff --git a/test_regress/t/t_unopt_converge_ndbg_bad.pl b/test_regress/t/t_unopt_converge_ndbg_bad.pl
new file mode 100755
index 000000000..a2cc6c968
--- /dev/null
+++ b/test_regress/t/t_unopt_converge_ndbg_bad.pl
@@ -0,0 +1,25 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# 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
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+scenarios(simulator => 1);
+
+top_filename("t/t_unopt_converge.v");
+
+compile(
+    v_flags2 => ['+define+ALLOW_UNOPT'],
+    make_flags => 'CPPFLAGS_ADD=-UVL_DEBUG',
+    );
+
+execute(
+    fails => 1,
+    expect_filename => $Self->{golden_filename},
+    ) if $Self->{vlt_all};
+
+ok(1);
+1;
diff --git a/test_regress/t/t_unopt_converge_print_bad.out b/test_regress/t/t_unopt_converge_print_bad.out
new file mode 100644
index 000000000..3cc147cb3
--- /dev/null
+++ b/test_regress/t/t_unopt_converge_print_bad.out
@@ -0,0 +1,5 @@
+-V{t#,#}- Verilated::debug is on. Message prefix indicates {<thread>,<sequence_number>}.
+-V{t#,#}+    Vt_unopt_converge_print_bad::_change_request
+-V{t#,#}        CHANGE: t/t_unopt_converge.v:18: x
+%Error: t/t_unopt_converge.v:6: Verilated model didn't converge
+Aborting...
diff --git a/test_regress/t/t_unopt_converge_print_bad.pl b/test_regress/t/t_unopt_converge_print_bad.pl
index 67c9ea5e9..b2d9c3bfe 100755
--- a/test_regress/t/t_unopt_converge_print_bad.pl
+++ b/test_regress/t/t_unopt_converge_print_bad.pl
@@ -19,7 +19,7 @@ compile(
 
 execute(
     fails => 1,
-    expect => '%Error: \S+:\d+: Verilated model didn\'t converge',
+    expect_filename => $Self->{golden_filename},
     ) if $Self->{vlt_all};
 
 ok(1);
diff --git a/test_regress/t/t_unopt_converge_run_bad.out b/test_regress/t/t_unopt_converge_run_bad.out
new file mode 100644
index 000000000..bd3150508
--- /dev/null
+++ b/test_regress/t/t_unopt_converge_run_bad.out
@@ -0,0 +1,5 @@
+-V{t#,#}- Verilated::debug is on. Message prefix indicates {<thread>,<sequence_number>}.
+-V{t#,#}+    Vt_unopt_converge_run_bad::_change_request
+-V{t#,#}        CHANGE: t/t_unopt_converge.v:18: x
+%Error: t/t_unopt_converge.v:6: Verilated model didn't converge
+Aborting...
diff --git a/test_regress/t/t_unopt_converge_run_bad.pl b/test_regress/t/t_unopt_converge_run_bad.pl
index 437291957..b6a17767b 100755
--- a/test_regress/t/t_unopt_converge_run_bad.pl
+++ b/test_regress/t/t_unopt_converge_run_bad.pl
@@ -17,7 +17,7 @@ compile(
 
 execute(
     fails => 1,
-    expect => '%Error: \S+:\d+: Verilated model didn\'t converge',
+    expect_filename => $Self->{golden_filename},
     ) if $Self->{vlt_all};
 
 ok(1);
diff --git a/test_regress/t/t_verilated_debug.out b/test_regress/t/t_verilated_debug.out
index fbfd8e09a..f1bcca561 100644
--- a/test_regress/t/t_verilated_debug.out
+++ b/test_regress/t/t_verilated_debug.out
@@ -1,24 +1,24 @@
--V{t0,1}- Verilated::debug is on. Message prefix indicates {<thread>,<sequence_number>}.
--V{t0,2}+    Vt_verilated_debug::_ctor_var_reset
+-V{t#,#}- Verilated::debug is on. Message prefix indicates {<thread>,<sequence_number>}.
+-V{t#,#}+    Vt_verilated_debug::_ctor_var_reset
 internalsDump:
   Version: Verilator ###
   Argv: obj_vlt/t_verilated_debug/Vt_verilated_debug
   scopesDump:
 
--V{t0,3}+++++TOP Evaluate Vt_verilated_debug::eval
--V{t0,4}+    Vt_verilated_debug::_eval_debug_assertions
--V{t0,5}+    Vt_verilated_debug::_eval_initial
--V{t0,6}+    Vt_verilated_debug::_eval_settle
--V{t0,7}+    Vt_verilated_debug::_eval
--V{t0,8}+    Vt_verilated_debug::_change_request
--V{t0,9}+ Clock loop
--V{t0,10}+    Vt_verilated_debug::_eval
--V{t0,11}+    Vt_verilated_debug::_change_request
--V{t0,12}+++++TOP Evaluate Vt_verilated_debug::eval
--V{t0,13}+    Vt_verilated_debug::_eval_debug_assertions
--V{t0,14}+ Clock loop
--V{t0,15}+    Vt_verilated_debug::_eval
--V{t0,16}+    Vt_verilated_debug::_sequent__TOP__1
+-V{t#,#}+++++TOP Evaluate Vt_verilated_debug::eval
+-V{t#,#}+    Vt_verilated_debug::_eval_debug_assertions
+-V{t#,#}+    Vt_verilated_debug::_eval_initial
+-V{t#,#}+    Vt_verilated_debug::_eval_settle
+-V{t#,#}+    Vt_verilated_debug::_eval
+-V{t#,#}+    Vt_verilated_debug::_change_request
+-V{t#,#}+ Clock loop
+-V{t#,#}+    Vt_verilated_debug::_eval
+-V{t#,#}+    Vt_verilated_debug::_change_request
+-V{t#,#}+++++TOP Evaluate Vt_verilated_debug::eval
+-V{t#,#}+    Vt_verilated_debug::_eval_debug_assertions
+-V{t#,#}+ Clock loop
+-V{t#,#}+    Vt_verilated_debug::_eval
+-V{t#,#}+    Vt_verilated_debug::_sequent__TOP__1
 *-* All Finished *-*
--V{t0,17}+    Vt_verilated_debug::_change_request
--V{t0,18}+    Vt_verilated_debug::final
+-V{t#,#}+    Vt_verilated_debug::_change_request
+-V{t#,#}+    Vt_verilated_debug::final