diff --git a/lib/completionlib.php b/lib/completionlib.php
index e72de6ed75d..451cd8a4bc6 100644
--- a/lib/completionlib.php
+++ b/lib/completionlib.php
@@ -1117,7 +1117,9 @@ class completion_info {
         // Custom activity module completion data.
 
         // Cast custom data to array before checking for custom completion rules.
-        $customdata = (array)$cm->customdata;
+        // We call ->get_custom_data() instead of ->customdata here because there is the chance of recursive calling,
+        // and we cannot call a getter from a getter in PHP.
+        $customdata = (array) $cm->get_custom_data();
         // Return early if the plugin does not define custom completion rules.
         if (empty($customdata['customcompletionrules'])) {
             return $data;
diff --git a/lib/modinfolib.php b/lib/modinfolib.php
index 02fe0b5f4ac..0949413b499 100644
--- a/lib/modinfolib.php
+++ b/lib/modinfolib.php
@@ -1420,9 +1420,14 @@ class cm_info implements IteratorAggregate {
         return $this->onclick;
     }
     /**
+     * Getter method for property $customdata, ensures that dynamic data is retrieved.
+     *
+     * This method is normally called by the property ->customdata, but can be called directly if there
+     * is a case when it might be called recursively (you can't call property values recursively).
+     *
      * @return mixed Optional custom data stored in modinfo cache for this activity, or null if none
      */
-    private function get_custom_data() {
+    public function get_custom_data() {
         $this->obtain_dynamic_data();
         return $this->customdata;
     }
@@ -1688,6 +1693,9 @@ class cm_info implements IteratorAggregate {
      * @param mixed $value The value
      */
     public function override_customdata($name, $value) {
+        if (!is_array($this->customdata)) {
+            $this->customdata = [];
+        }
         $this->customdata[$name] = $value;
     }
 
@@ -1893,7 +1901,8 @@ class cm_info implements IteratorAggregate {
      * the module or not.
      *
      * As part of this function, the module's _cm_info_dynamic function from its lib.php will
-     * be called (if it exists).
+     * be called (if it exists). Make sure that the functions that are called here do not use
+     * any getter magic method from cm_info.
      * @return void
      */
     private function obtain_dynamic_data() {
diff --git a/mod/folder/lib.php b/mod/folder/lib.php
index c450915cb1d..2fe3f23e0f6 100644
--- a/mod/folder/lib.php
+++ b/mod/folder/lib.php
@@ -439,7 +439,7 @@ function folder_get_coursemodule_info($cm) {
  * @param cm_info $cm
  */
 function folder_cm_info_dynamic(cm_info $cm) {
-    if ($cm->customdata) {
+    if ($cm->get_custom_data()) {
         // the field 'customdata' is not empty IF AND ONLY IF we display contens inline
         $cm->set_no_view_link();
     }