diff --git a/mod/quiz/addrandomform.php b/mod/quiz/addrandomform.php
index eec332d0268..6121d874662 100644
--- a/mod/quiz/addrandomform.php
+++ b/mod/quiz/addrandomform.php
@@ -106,7 +106,8 @@ class quiz_add_random_form extends moodleform {
         // Add the javascript required to enhance this mform.
         $PAGE->requires->js_call_amd('mod_quiz/add_random_form', 'init', [
             $mform->getAttribute('id'),
-            $contexts->lowest()->id
+            $contexts->lowest()->id,
+            $tops
         ]);
     }
 
diff --git a/mod/quiz/amd/build/add_random_form.min.js b/mod/quiz/amd/build/add_random_form.min.js
index 03d7365bec4..977a623131c 100644
--- a/mod/quiz/amd/build/add_random_form.min.js
+++ b/mod/quiz/amd/build/add_random_form.min.js
@@ -1 +1 @@
-define(["jquery","mod_quiz/random_question_form_preview"],function(a,b){var c=2e3,d={PREVIEW_CONTAINER:'[data-region="random-question-preview-container"]',CATEGORY_FORM_ELEMENT:'[name="category"]',SUBCATEGORY_FORM_ELEMENT:'[name="includesubcategories"]',TAG_IDS_FORM_ELEMENT:'[name="fromtags[]"]'},e=function(a){var b=a.find(d.CATEGORY_FORM_ELEMENT).val(),c=b.split(",");return c[0]},f=function(a){return a.find(d.SUBCATEGORY_FORM_ELEMENT).is(":checked")},g=function(a){var b=a.find(d.TAG_IDS_FORM_ELEMENT).val();return b.map(function(a){var b=a.split(",");return b[0]})},h=function(a,c){var h=a.find(d.PREVIEW_CONTAINER);b.reload(h,e(a),f(a),g(a),c)},i=function(a){return a.closest(d.CATEGORY_FORM_ELEMENT).length>0||(a.closest(d.SUBCATEGORY_FORM_ELEMENT).length>0||a.closest(d.TAG_IDS_FORM_ELEMENT).length>0)},j=function(d,e){var f=null;d.on("change",function(g){i(a(g.target))&&(b.showLoadingIcon(d),f&&clearTimeout(f),f=setTimeout(function(){h(d,e)},c))})},k=function(b,c){var d=a("#"+b);h(d,c),j(d,c)};return{init:k}});
\ No newline at end of file
+define(["jquery","mod_quiz/random_question_form_preview"],function(a,b){var c=2e3,d={PREVIEW_CONTAINER:'[data-region="random-question-preview-container"]',CATEGORY_FORM_ELEMENT:'[name="category"]',SUBCATEGORY_FORM_ELEMENT:'[name="includesubcategories"]',TAG_IDS_FORM_ELEMENT:'[name="fromtags[]"]'},e=function(a){return a.find(d.CATEGORY_FORM_ELEMENT).val()},f=function(a){var b=e(a),c=b.split(",");return c[0]},g=function(a,b){var c=e(a);return b.indexOf(c)>-1},h=function(a,b){return!!g(a,b)||a.find(d.SUBCATEGORY_FORM_ELEMENT).is(":checked")},i=function(a){var b=a.find(d.TAG_IDS_FORM_ELEMENT).val();return b.map(function(a){var b=a.split(",");return b[0]})},j=function(a,c,e){var g=a.find(d.PREVIEW_CONTAINER);b.reload(g,f(a),h(a,e),i(a),c)},k=function(a){return a.closest(d.CATEGORY_FORM_ELEMENT).length>0||(a.closest(d.SUBCATEGORY_FORM_ELEMENT).length>0||a.closest(d.TAG_IDS_FORM_ELEMENT).length>0)},l=function(d,e,f){var g=null;d.on("change",function(h){k(a(h.target))&&(b.showLoadingIcon(d),g&&clearTimeout(g),g=setTimeout(function(){j(d,e,f)},c))})},m=function(b,c,d){var e=a("#"+b);j(e,c,d),l(e,c,d)};return{init:m}});
\ No newline at end of file
diff --git a/mod/quiz/amd/src/add_random_form.js b/mod/quiz/amd/src/add_random_form.js
index b2a4b308835..35ebd32d0f7 100644
--- a/mod/quiz/amd/src/add_random_form.js
+++ b/mod/quiz/amd/src/add_random_form.js
@@ -41,6 +41,16 @@ define(
         TAG_IDS_FORM_ELEMENT: '[name="fromtags[]"]'
     };
 
+    /**
+     * Get the selected category value from the form.
+     *
+     * @param {jquery} form The form element.
+     * @return {string} The category value.
+     */
+    var getCategorySelectValue = function(form) {
+        return form.find(SELECTORS.CATEGORY_FORM_ELEMENT).val();
+    };
+
     /**
      * Get the category id from the form.
      *
@@ -50,22 +60,39 @@ define(
     var getCategoryId = function(form) {
         // The value string is the category id and category context id joined
         // by a comma.
-        var valueString = form.find(SELECTORS.CATEGORY_FORM_ELEMENT).val();
+        var valueString = getCategorySelectValue(form);
         // Split the two ids.
         var values = valueString.split(',');
         // Return just the category id.
         return values[0];
     };
 
+    /**
+     * Check if a top level category is selected in the form.
+     *
+     * @param {jquery} form The form element.
+     * @param {string[]} topCategories List of top category values (matching the select box values)
+     * @return {bool}
+     */
+    var isTopLevelCategorySelected = function(form, topCategories) {
+        var selectedValue = getCategorySelectValue(form);
+        return (topCategories.indexOf(selectedValue) > -1);
+    };
+
     /**
      * Check if the form indicates we should include include subcategories in
      * the filter.
      *
      * @param {jquery} form The form element.
+     * @param {string[]} topCategories List of top category values (matching the select box values)
      * @return {bool}
      */
-    var shouldIncludeSubcategories = function(form) {
-        return form.find(SELECTORS.SUBCATEGORY_FORM_ELEMENT).is(':checked');
+    var shouldIncludeSubcategories = function(form, topCategories) {
+        if (isTopLevelCategorySelected(form, topCategories)) {
+            return true;
+        } else {
+            return form.find(SELECTORS.SUBCATEGORY_FORM_ELEMENT).is(':checked');
+        }
     };
 
     /**
@@ -89,13 +116,14 @@ define(
      *
      * @param {jquery} form The form element.
      * @param {int} contextId The current context id.
+     * @param {string[]} topCategories List of top category values (matching the select box values)
      */
-    var reloadQuestionPreview = function(form, contextId) {
+    var reloadQuestionPreview = function(form, contextId, topCategories) {
         var previewContainer = form.find(SELECTORS.PREVIEW_CONTAINER);
         RandomQuestionFormPreview.reload(
             previewContainer,
             getCategoryId(form),
-            shouldIncludeSubcategories(form),
+            shouldIncludeSubcategories(form, topCategories),
             getTagIds(form),
             contextId
         );
@@ -136,8 +164,9 @@ define(
      *
      * @param {jquery} form The form element.
      * @param {int} contextId The current context id.
+     * @param {string[]} topCategories List of top category values (matching the select box values)
      */
-    var addEventListeners = function(form, contextId) {
+    var addEventListeners = function(form, contextId, topCategories) {
         var reloadTimerId = null;
 
         form.on('change', function(e) {
@@ -160,7 +189,7 @@ define(
             // in case the user is still modifying the form. We don't want to
             // spam reload requests.
             reloadTimerId = setTimeout(function() {
-                reloadQuestionPreview(form, contextId);
+                reloadQuestionPreview(form, contextId, topCategories);
             }, RELOAD_DELAY);
         });
     };
@@ -171,12 +200,13 @@ define(
      *
      * @param {jquery} formId The form element id.
      * @param {int} contextId The current context id.
+     * @param {string[]} topCategories List of top category values (matching the select box values)
      */
-    var init = function(formId, contextId) {
+    var init = function(formId, contextId, topCategories) {
         var form = $('#' + formId);
 
-        reloadQuestionPreview(form, contextId);
-        addEventListeners(form, contextId);
+        reloadQuestionPreview(form, contextId, topCategories);
+        addEventListeners(form, contextId, topCategories);
     };
 
     return {