diff --git a/classes/local/controllers/maintenance_static_page.php b/classes/local/controllers/maintenance_static_page.php
index c231b24..01c431f 100644
--- a/classes/local/controllers/maintenance_static_page.php
+++ b/classes/local/controllers/maintenance_static_page.php
@@ -28,7 +28,6 @@ namespace auth_outage\local\controllers;
 use auth_outage\local\outage;
 use coding_exception;
 use DOMDocument;
-use DOMElement;
 use invalid_parameter_exception;
 use moodle_url;
 
@@ -43,9 +42,6 @@ defined('MOODLE_INTERNAL') || die();
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class maintenance_static_page {
-    /** @var int */
-    private static $nextfile = 1;
-
     /**
      * Gets the cli maintenance template file location.
      * @return string
@@ -199,18 +195,17 @@ class maintenance_static_page {
             return $url; // External URL, leave it.
         }
 
-        $file = self::$nextfile++;
-        if ($type != '') {
-            $file .= '.'.$type;
-        }
-        $path = self::get_resources_folder().'/'.$file;
-
         // PHPUnit will use www.example.com as wwwroot and we don't to copy the file.
-        if (!PHPUNIT_TEST) {
-            copy($url, $path);
+        if (PHPUNIT_TEST) {
+            $contents = '';
+        } else {
+            $contents = file_get_contents($url);
         }
+        $filename = sha1($contents).'.'.$type;
+        $filepath = self::get_resources_folder().'/'.$filename;
+        file_put_contents($filepath, $contents);
 
-        $url = (string)new moodle_url('/auth/outage/maintenance.php?file='.$file);
+        $url = (string)new moodle_url('/auth/outage/maintenance.php?file='.$filename);
         return $url;
     }
 }
diff --git a/maintenance.php b/maintenance.php
index 6db5925..902b193 100644
--- a/maintenance.php
+++ b/maintenance.php
@@ -44,12 +44,15 @@ if (isset($_GET['file'])) {
     }
 
     // Detect type, we only support css or PNG images.
-    $type = substr($file, -3);
-    if ($type == 'css') {
-        header('Content-type: text/css');
-    } else {
-        header('Content-type: image/png');
-    }
+    header('Content-Type: '.(substr($file, -3) == 'css' ? 'text/css' : 'image/png'));
+
+    // Use cache.
+    $lifetime = 60 * 60 * 24; // 1 day.
+    header('Expires: '. gmdate('D, d M Y H:i:s', time() + $lifetime) .' GMT');
+    header('Pragma: ');
+    header('Cache-Control: public, max-age='.$lifetime);
+    header('Accept-Ranges: none');
+
     readfile($file);
     return;
 }
diff --git a/tests/phpunit/local/controllers/maintenance_static_page_test.php b/tests/phpunit/local/controllers/maintenance_static_page_test.php
index e5a8d35..815cc0a 100644
--- a/tests/phpunit/local/controllers/maintenance_static_page_test.php
+++ b/tests/phpunit/local/controllers/maintenance_static_page_test.php
@@ -88,7 +88,7 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
         maintenance_static_page::create_from_html($html);
         $generated = file_get_contents(maintenance_static_page::get_template_file());
 
-        self::assertContains('http://www.example.com/moodle/auth/outage/maintenance.php/', $generated);
+        self::assertContains('http://www.example.com/moodle/auth/outage/maintenance.php?file=', $generated);
         self::assertNotContains($link1, $generated);
         self::assertNotContains($link2, $generated);
         self::assertContains($link3, $generated);
@@ -104,7 +104,7 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
         maintenance_static_page::create_from_html($html);
         $generated = file_get_contents(maintenance_static_page::get_template_file());
 
-        self::assertContains('http://www.example.com/moodle/auth/outage/maintenance.php/', $generated);
+        self::assertContains('http://www.example.com/moodle/auth/outage/maintenance.php?file=', $generated);
         self::assertNotContains($link1, $generated);
         self::assertNotContains($link2, $generated);
         self::assertContains($link3, $generated);
@@ -119,6 +119,6 @@ class maintenance_static_page_test extends auth_outage_base_testcase {
         $generated = file_get_contents(maintenance_static_page::get_template_file());
 
         self::assertNotContains($link, $generated);
-        self::assertContains('http://www.example.com/moodle/auth/outage/maintenance.php/', $generated);
+        self::assertContains('http://www.example.com/moodle/auth/outage/maintenance.php?file=', $generated);
     }
 }