diff --git a/mod/forum/externallib.php b/mod/forum/externallib.php
index cabc35051f9..a6f246c07ab 100644
--- a/mod/forum/externallib.php
+++ b/mod/forum/externallib.php
@@ -268,14 +268,20 @@ class mod_forum_external extends external_api {
                 $post->children = array();
             }
 
-            $user = new stdclass();
-            $user->id = $post->userid;
-            $user = username_load_fields_from_object($user, $post, null, array('picture', 'imagealt', 'email'));
-            $post->userfullname = fullname($user, $canviewfullname);
+            if (forum_is_author_hidden($post, $forum)) {
+                $post->userid = null;
+                $post->userfullname = null;
+                $post->userpictureurl = null;
+            } else {
+                $user = new stdclass();
+                $user->id = $post->userid;
+                $user = username_load_fields_from_object($user, $post, null, array('picture', 'imagealt', 'email'));
+                $post->userfullname = fullname($user, $canviewfullname);
 
-            $userpicture = new user_picture($user);
-            $userpicture->size = 1; // Size f1.
-            $post->userpictureurl = $userpicture->get_url($PAGE)->out(false);
+                $userpicture = new user_picture($user);
+                $userpicture->size = 1; // Size f1.
+                $post->userpictureurl = $userpicture->get_url($PAGE)->out(false);
+            }
 
             $post->subject = external_format_string($post->subject, $modcontext->id);
             // Rewrite embedded images URLs.
@@ -467,31 +473,6 @@ class mod_forum_external extends external_api {
                     $discussion->numreplies = (int) $replies[$discussion->discussion]->replies;
                 }
 
-                $picturefields = explode(',', user_picture::fields());
-
-                // Load user objects from the results of the query.
-                $user = new stdclass();
-                $user->id = $discussion->userid;
-                $user = username_load_fields_from_object($user, $discussion, null, $picturefields);
-                // Preserve the id, it can be modified by username_load_fields_from_object.
-                $user->id = $discussion->userid;
-                $discussion->userfullname = fullname($user, $canviewfullname);
-
-                $userpicture = new user_picture($user);
-                $userpicture->size = 1; // Size f1.
-                $discussion->userpictureurl = $userpicture->get_url($PAGE)->out(false);
-
-                $usermodified = new stdclass();
-                $usermodified->id = $discussion->usermodified;
-                $usermodified = username_load_fields_from_object($usermodified, $discussion, 'um', $picturefields);
-                // Preserve the id (it can be overwritten due to the prefixed $picturefields).
-                $usermodified->id = $discussion->usermodified;
-                $discussion->usermodifiedfullname = fullname($usermodified, $canviewfullname);
-
-                $userpicture = new user_picture($usermodified);
-                $userpicture->size = 1; // Size f1.
-                $discussion->usermodifiedpictureurl = $userpicture->get_url($PAGE)->out(false);
-
                 $discussion->name = external_format_string($discussion->name, $modcontext->id);
                 $discussion->subject = external_format_string($discussion->subject, $modcontext->id);
                 // Rewrite embedded images URLs.
@@ -512,6 +493,41 @@ class mod_forum_external extends external_api {
                 $discussion->locked = forum_discussion_is_locked($forum, $discussion);
                 $discussion->canreply = forum_user_can_post($forum, $discussion, $USER, $cm, $course, $modcontext);
 
+                if (forum_is_author_hidden($discussion, $forum)) {
+                    $discussion->userid = null;
+                    $discussion->userfullname = null;
+                    $discussion->userpictureurl = null;
+
+                    $discussion->usermodified = null;
+                    $discussion->usermodifiedfullname = null;
+                    $discussion->usermodifiedpictureurl = null;
+                } else {
+                    $picturefields = explode(',', user_picture::fields());
+
+                    // Load user objects from the results of the query.
+                    $user = new stdclass();
+                    $user->id = $discussion->userid;
+                    $user = username_load_fields_from_object($user, $discussion, null, $picturefields);
+                    // Preserve the id, it can be modified by username_load_fields_from_object.
+                    $user->id = $discussion->userid;
+                    $discussion->userfullname = fullname($user, $canviewfullname);
+
+                    $userpicture = new user_picture($user);
+                    $userpicture->size = 1; // Size f1.
+                    $discussion->userpictureurl = $userpicture->get_url($PAGE)->out(false);
+
+                    $usermodified = new stdclass();
+                    $usermodified->id = $discussion->usermodified;
+                    $usermodified = username_load_fields_from_object($usermodified, $discussion, 'um', $picturefields);
+                    // Preserve the id (it can be overwritten due to the prefixed $picturefields).
+                    $usermodified->id = $discussion->usermodified;
+                    $discussion->usermodifiedfullname = fullname($usermodified, $canviewfullname);
+
+                    $userpicture = new user_picture($usermodified);
+                    $userpicture->size = 1; // Size f1.
+                    $discussion->usermodifiedpictureurl = $userpicture->get_url($PAGE)->out(false);
+                }
+
                 $discussions[] = $discussion;
             }
         }