diff --git a/admin/settings/users.php b/admin/settings/users.php
index b7f1e257947..07835992d12 100644
--- a/admin/settings/users.php
+++ b/admin/settings/users.php
@@ -151,6 +151,7 @@ if ($hassiteconfig
                     'institution' => new lang_string('institution'),
                 )));
         $temp->add(new admin_setting_configcheckbox('enablegravatar', new lang_string('enablegravatar', 'admin'), new lang_string('enablegravatar_help', 'admin'), 0));
+        $temp->add(new admin_setting_configtext('gravatardefaulturl', new lang_string('gravatardefaulturl', 'admin'), new lang_string('gravatardefaulturl_help', 'admin'), 'mm'));
     }
 
     $ADMIN->add('roles', $temp);
diff --git a/lang/en/admin.php b/lang/en/admin.php
index aa0ecca784f..b67ce851629 100644
--- a/lang/en/admin.php
+++ b/lang/en/admin.php
@@ -553,6 +553,8 @@ $string['googlemapkey3_help'] = 'You need to enter a special key to use Google M
 $string['gotofirst'] = 'Go to first missing string';
 $string['gradebook'] = 'Gradebook';
 $string['gradebookroles'] = 'Graded roles';
+$string['gravatardefaulturl'] = 'Gravatar default image URL';
+$string['gravatardefaulturl_help'] = 'Gravatar needs a default image to display if it is unable to find a picture for a given user. Provide a full URL for an image. If you leave this setting empty, Moodle will attempt to use the most appropriate default image for the page you are viewing. Note also that Gravatar has a number of codes which can be used to <a href="https://en.gravatar.com/site/implement/images/#default-image">generate default images</a>.';
 $string['gradeexport'] = 'Primary grade export methods';
 $string['guestroleid'] = 'Role for guest';
 $string['guestroleid_help'] = 'This role is automatically assigned to the guest user. It is also temporarily assigned to not enrolled users that enter the course via guest enrolment plugin.';
diff --git a/lib/outputcomponents.php b/lib/outputcomponents.php
index c10caffb1c4..3c05b452a80 100644
--- a/lib/outputcomponents.php
+++ b/lib/outputcomponents.php
@@ -384,12 +384,25 @@ class user_picture implements renderable {
             // Hash the users email address
             $md5 = md5(strtolower(trim($this->user->email)));
             // Build a gravatar URL with what we know.
+
+            // Find the best default image URL we can (MDL-35669)
+            if (empty($CFG->gravatardefaulturl)) {
+                $absoluteimagepath = $page->theme->resolve_image_location('u/'.$filename, 'core');
+                if (strpos($absoluteimagepath, $CFG->dirroot) === 0) {
+                    $gravatardefault = $CFG->wwwroot . substr($absoluteimagepath, strlen($CFG->dirroot));
+                } else {
+                    $gravatardefault = $CFG->wwwroot . '/pix/u/' . $filename . '.png';
+                }
+            } else {
+                $gravatardefault = $CFG->gravatardefaulturl;
+            }
+
             // If the currently requested page is https then we'll return an
             // https gravatar page.
             if (strpos($CFG->httpswwwroot, 'https:') === 0) {
-                return new moodle_url("https://secure.gravatar.com/avatar/{$md5}", array('s' => $size, 'd' => $defaulturl->out(false)));
+                return new moodle_url("https://secure.gravatar.com/avatar/{$md5}", array('s' => $size, 'd' => $gravatardefault));
             } else {
-                return new moodle_url("http://www.gravatar.com/avatar/{$md5}", array('s' => $size, 'd' => $defaulturl->out(false)));
+                return new moodle_url("http://www.gravatar.com/avatar/{$md5}", array('s' => $size, 'd' => $gravatardefault));
             }
         }