diff --git a/lib/dml/moodle_database.php b/lib/dml/moodle_database.php
index 091fdeff374..4621c731ed3 100644
--- a/lib/dml/moodle_database.php
+++ b/lib/dml/moodle_database.php
@@ -889,9 +889,6 @@ abstract class moodle_database {
         // convert table names
         $sql = $this->fix_table_names($sql);
 
-        // Optionally add debug trace to sql as a comment.
-        $sql = $this->add_sql_debugging($sql);
-
         // cast booleans to 1/0 int and detect forbidden objects
         foreach ($params as $key => $value) {
             $this->detect_objects($value);
@@ -903,6 +900,9 @@ abstract class moodle_database {
         $dollar_count = preg_match_all('/\$[1-9][0-9]*/', $sql, $dollar_matches);
         $q_count     = substr_count($sql, '?');
 
+        // Optionally add debug trace to sql as a comment.
+        $sql = $this->add_sql_debugging($sql);
+
         $count = 0;
 
         if ($named_count) {
diff --git a/lib/dml/tests/dml_test.php b/lib/dml/tests/dml_test.php
index 95341605a15..3e950457c72 100644
--- a/lib/dml/tests/dml_test.php
+++ b/lib/dml/tests/dml_test.php
@@ -519,6 +519,30 @@ EOD;
         $CFG->debugsqltrace = 0;
     }
 
+    /**
+     * Test the database debugging as SQL comment in anon class
+     *
+     * @covers ::add_sql_debugging
+     */
+    public function test_sql_debugging_anon_class() {
+        global $CFG;
+        $CFG->debugsqltrace = 100;
+
+        // A anon class.
+        $another = new class {
+            /**
+             * Just a test log function
+             */
+            public function log() {
+                global $DB;
+                $DB->get_records_sql('SELECT firstname FROM {user} WHERE firstname = :firstname', ['firstname' => 'JohnDoe']);
+            }
+        };
+        $another->log();
+        $CFG->debugsqltrace = 0;
+        // No assertions just it should not error.
+    }
+
     public function test_strtok() {
         // Strtok was previously used by bound emulation, make sure it is not used any more.
         $DB = $this->tdb;
diff --git a/lib/setuplib.php b/lib/setuplib.php
index aacdb699948..d1065dc8150 100644
--- a/lib/setuplib.php
+++ b/lib/setuplib.php
@@ -714,18 +714,23 @@ function format_backtrace($callers, $plaintext = false) {
         if (!isset($caller['file'])) {
             $caller['file'] = 'unknownfile'; // probably call_user_func()
         }
-        $from .= $plaintext ? '* ' : '<li>';
-        $from .= 'line ' . $caller['line'] . ' of ' . str_replace($dirroot, '', $caller['file']);
+        $line = $plaintext ? '* ' : '<li>';
+        $line .= 'line ' . $caller['line'] . ' of ' . str_replace($dirroot, '', $caller['file']);
         if (isset($caller['function'])) {
-            $from .= ': call to ';
+            $line .= ': call to ';
             if (isset($caller['class'])) {
-                $from .= $caller['class'] . $caller['type'];
+                $line .= $caller['class'] . $caller['type'];
             }
-            $from .= $caller['function'] . '()';
+            $line .= $caller['function'] . '()';
         } else if (isset($caller['exception'])) {
-            $from .= ': '.$caller['exception'].' thrown';
+            $line .= ': '.$caller['exception'].' thrown';
         }
-        $from .= $plaintext ? "\n" : '</li>';
+
+        // Remove any non printable chars.
+        $line = preg_replace('/[[:^print:]]/', '', $line);
+
+        $line .= $plaintext ? "\n" : '</li>';
+        $from .= $line;
     }
     $from .= $plaintext ? '' : '</ul>';