diff --git a/lib/classes/dml/recordset_walk.php b/lib/classes/dml/recordset_walk.php
index 7e9ea692887fc..3d560cf8fd2bf 100644
--- a/lib/classes/dml/recordset_walk.php
+++ b/lib/classes/dml/recordset_walk.php
@@ -57,7 +57,7 @@ class recordset_walk implements \Iterator {
     protected $callback;
 
     /**
-     * @var array|false Extra params for the callback.
+     * @var mixed|null Extra param for the callback.
      */
     protected $callbackextra;
 
@@ -66,9 +66,9 @@ class recordset_walk implements \Iterator {
      *
      * @param \moodle_recordset $recordset Recordset to iterate.
      * @param callable $callback Apply this function to each record. If using a method, it should be public.
-     * @param array $callbackextra Array of arguments to pass to the callback.
+     * @param mixed $callbackextra An extra single parameter to pass to the callback. Use a container to pass multiple values.
      */
-    public function __construct(\moodle_recordset $recordset, callable $callback, $callbackextra = false) {
+    public function __construct(\moodle_recordset $recordset, callable $callback, $callbackextra = null) {
         $this->recordset = $recordset;
         $this->callback = $callback;
         $this->callbackextra = $callbackextra;
@@ -99,10 +99,10 @@ public function current() {
         }
 
         // Apply callback and return.
-        if ($this->callbackextra) {
-            return call_user_func($this->callback, $record);
-        } else {
+        if (!is_null($this->callbackextra)) {
             return call_user_func($this->callback, $record, $this->callbackextra);
+        } else {
+            return call_user_func($this->callback, $record);
         }
     }
 
diff --git a/lib/dml/tests/recordset_walk_test.php b/lib/dml/tests/recordset_walk_test.php
index bd9c804a449da..bab70450a55dc 100644
--- a/lib/dml/tests/recordset_walk_test.php
+++ b/lib/dml/tests/recordset_walk_test.php
@@ -45,11 +45,14 @@ public function test_no_data() {
 
         $recordset = $DB->get_recordset('assign');
         $walker = new \core\dml\recordset_walk($recordset, array($this, 'simple_callback'));
-        $this->assertEquals(0, iterator_count($walker));
         $this->assertFalse($walker->valid());
+
+        $count = 0;
         foreach ($walker as $data) {
             // No error here.
+            $count++;
         }
+        $this->assertEquals(0, $count);
         $walker->close();
     }
 
@@ -65,11 +68,14 @@ public function test_simple_callback() {
         // Simple iteration.
         $recordset = $DB->get_recordset('assign');
         $walker = new \core\dml\recordset_walk($recordset, array($this, 'simple_callback'));
-        $this->assertEquals(10, iterator_count($walker));
+
+        $count = 0;
         foreach ($walker as $data) {
             // Checking that the callback is being executed on each iteration.
             $this->assertEquals($data->id . ' potatoes', $data->newfield);
+            $count++;
         }
+        $this->assertEquals(10, $count);
         // No exception if we double-close.
         $walker->close();
     }
@@ -85,17 +91,22 @@ public function test_extra_params_callback() {
 
         // Iteration with extra callback arguments.
         $recordset = $DB->get_recordset('assign');
+
         $walker = new \core\dml\recordset_walk(
             $recordset,
             array($this, 'extra_callback'),
             array('brown' => 'onions')
         );
-        $this->assertEquals(10, iterator_count($walker));
+
+        $count = 0;
         foreach ($walker as $data) {
             // Checking that the callback is being executed on each
             // iteration and the param is being passed.
             $this->assertEquals('onions', $data->brown);
+            $count++;
         }
+        $this->assertEquals(10, $count);
+
         $walker->close();
     }
 
@@ -105,7 +116,9 @@ public function test_extra_params_callback() {
      * @param stdClass $data
      * @return \Traversable
      */
-    public function simple_callback($data) {
+    public function simple_callback($data, $nothing = 'notpassed') {
+        // Confirm nothing was passed.
+        $this->assertEquals('notpassed', $nothing);
         $data->newfield = $data->id . ' potatoes';
         return $data;
     }