diff --git a/bin/verilator b/bin/verilator
index 79a9ffd59..15d399587 100755
--- a/bin/verilator
+++ b/bin/verilator
@@ -3914,7 +3914,19 @@ checking across the designs, and prevents other users from compiling your
 code without knowing the magic set of disables needed to successfully
 compile your design.
 
-List of all warnings:
+=head2 Error and Warning Format
+
+Warnings and errors printed by Verilator always match this regular
+expression:
+
+        %(Error|Warning)(-[A-Z0-9_]+)?: ((\S+):(\d+):((\d+):)?)? .*
+
+Errors and warning start with a percent sign (historical heritage from
+Digital Equipment Corporation).  Some errors or warning have a code
+attached, with meanings described below.  Some errors also have a filename,
+line number and optional column number (starting at column 1 to match GCC).
+
+=head2 List of all warnings
 
 =over 4
 
diff --git a/src/V3FileLine.cpp b/src/V3FileLine.cpp
index 7dad8ea66..ccf065b73 100644
--- a/src/V3FileLine.cpp
+++ b/src/V3FileLine.cpp
@@ -376,8 +376,11 @@ string FileLine::warnOther() const {
 
 string FileLine::source() const {
     if (VL_UNCOVERABLE(!m_contentp)) {
-        if (debug() || v3Global.opt.debugCheck()) return "%Error-internal-no-contents";
-        else return "";
+        if (debug() || v3Global.opt.debugCheck()) {
+            return "%Error: internal tracking of file contents failed";
+        } else {
+            return "";
+        }
     }
     return m_contentp->getLine(m_contentLineno);
 }
diff --git a/test_regress/t/t_dist_error_format.pl b/test_regress/t/t_dist_error_format.pl
new file mode 100755
index 000000000..af97e7be6
--- /dev/null
+++ b/test_regress/t/t_dist_error_format.pl
@@ -0,0 +1,74 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 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.
+
+use IO::File;
+
+scenarios(dist => 1);
+
+my $root = "..";
+my $Debug;
+
+if (!-r "$root/.git") {
+    skip("Not in a git repository");
+} else {
+    formats();
+}
+
+ok(1);
+
+# Check all error messages match our standard format
+# This assumes .out files cover all important errors
+
+sub formats {
+    my $files = "../test_regress/t/*.out";
+    my %warns;
+    my $lnmatch = 0;
+    foreach my $file (glob $files) {
+        my $wholefile = file_contents($file);
+        $file =~ s!.*/!!;
+        if ($wholefile =~ /Exiting due to/
+            || $wholefile =~ /%(Error|Warning)/) {
+            my $lineno = 0;
+            foreach my $line (split /\n/, $wholefile) {
+                ++$lineno;
+                if ($line =~ /(Error|Warning)/) {
+                    # These formats are documented in bin/verilator
+                    # Error with fileline
+                    # For testing only: we assume no : in filename
+                    my $match = $line;
+                    $match =~ s/^\[\d+\] //;  # Simplify runtime errors
+                    if ($match =~ /^%(Error|Warning)(-[A-Z0-9_]+)?: ([^:]+):(\d+):((\d+):)? /) {
+                        ++$lnmatch;
+                        print "ok-el $file $line\n" if $Self->{verbose};
+                    }
+                    # Error no fileline
+                    # For testing only: we assume any : is single quoted
+                    elsif ($match =~ /^%(Error|Warning)(-[A-Z0-9_]+)?: [^:']+/) {
+                        print "ok-en $file $line\n" if $Self->{verbose};
+                    }
+                    else {
+                        #print "FF $file $line\n";
+                        $warns{$file.":".$lineno} =
+                            "Non-standard warning/error: $file:$lineno: $line";
+                    }
+                }
+            }
+        }
+    }
+    $lnmatch or error("Check line number regexp is correct, no matches");
+    if (keys %warns) {
+        # First warning lists everything as that's shown in the driver summary
+        error($summary." ",join(' ',sort keys %warns));
+        foreach my $file (sort keys %warns) {
+            error($warns{$file});
+        }
+    }
+}
+
+1;
diff --git a/test_regress/t/t_interface_modport_dir_bad.out b/test_regress/t/t_interface_modport_dir_bad.out
index 8ea68f01f..927f0c16e 100644
--- a/test_regress/t/t_interface_modport_dir_bad.out
+++ b/test_regress/t/t_interface_modport_dir_bad.out
@@ -1,12 +1,12 @@
-#Expecting something along the line of:
+Expecting something along the line of:
 
-    %Error: t/t_interface_modport_dir_bad.v:36: Attempt to drive input-only modport: 'data'
-    : ... In instance t.source_i.source_i
-    ctrl.data <= ~ctrl.data;
-    ^~~~
-    %Error: Exiting due to 1 error(s)
-    %Error: t/t_interface_modport_dir_bad.v:37: Attempt to drive input-only modport: 'valid'
-    : ... In instance t.source_i.source_i
-    ctrl.valid<= ~ctrl.valid;
-    ^~~~
-    %Error: Exiting due to 1 error(s)
+%Error: t/t_interface_modport_dir_bad.v:36: Attempt to drive input-only modport: 'data'
+: ... In instance t.source_i.source_i
+ctrl.data <= ~ctrl.data;
+^~~~
+%Error: Exiting due to 1 error(s)
+%Error: t/t_interface_modport_dir_bad.v:37: Attempt to drive input-only modport: 'valid'
+: ... In instance t.source_i.source_i
+ctrl.valid<= ~ctrl.valid;
+^~~~
+%Error: Exiting due to 1 error(s)
diff --git a/test_regress/t/t_pp_line_bad.out b/test_regress/t/t_pp_line_bad.out
index 609b3befb..e88ab8e47 100644
--- a/test_regress/t/t_pp_line_bad.out
+++ b/test_regress/t/t_pp_line_bad.out
@@ -5,7 +5,7 @@
 `line 100
 ^
 %Error: somefile:100: `line was not properly formed with '`line number "filename" level'
-%Error-internal-no-contents
+%Error: internal tracking of file contents failed
 ^
 %Error: t/t_pp_line_bad.v:6: Define or directive not defined: '`line'
 `line