diff --git a/admin/settings/development.php b/admin/settings/development.php
index b99d519640b..a1ad6e02bfc 100644
--- a/admin/settings/development.php
+++ b/admin/settings/development.php
@@ -27,6 +27,9 @@ if ($hassiteconfig) { // speedup for non-admins, add all caps used on this page
     $temp->add(new admin_setting_configcheckbox('enabletgzbackups',
             new lang_string('enabletgzbackups', 'admin'),
             new lang_string('enabletgzbackups_desc', 'admin'), 0));
+    $temp->add(new admin_setting_php_extension_enabled('zlibenabled',
+            get_string('zlibenabled', 'admin'),
+            get_string('enabletgzbackups_nozlib', 'admin'), 'zlib'));
 
     $ADMIN->add('experimental', $temp);
 
diff --git a/lang/en/admin.php b/lang/en/admin.php
index 1d06ba401dd..34b8fa658b1 100644
--- a/lang/en/admin.php
+++ b/lang/en/admin.php
@@ -491,6 +491,7 @@ $string['enablesafebrowserintegration'] = 'Enable Safe Exam Browser integration'
 $string['enablestats'] = 'Enable statistics';
 $string['enabletgzbackups'] = 'Enable new backup format';
 $string['enabletgzbackups_desc'] = 'If enabled, future backups will be created in a new compression format for .mbz files (internally stored as a .tar.gz file). This removes the 4GB backup size restriction and may improve performance. Restore supports both formats and the difference should be transparent to users.';
+$string['enabletgzbackups_nozlib'] = 'PHP extension ‘zlib’ is not available. The new backup format relies on this extension and will be disabled until zlib is installed and enabled.';
 $string['enabletrusttext'] = 'Enable trusted content';
 $string['enablewebservices'] = 'Enable web services';
 $string['enablewsdocumentation'] = 'Web services documentation';
@@ -1130,6 +1131,7 @@ $string['webproxyinfo'] = 'Fill in following options if your Moodle server can n
 $string['xmlrpcrecommended'] = 'The xmlrpc extension is needed for hub communication, and useful for web services and Moodle networking';
 $string['yuicomboloading'] = 'YUI combo loading';
 $string['ziprequired'] = 'The Zip PHP extension is now required by Moodle, info-ZIP binaries or PclZip library are not used anymore.';
+$string['zlibenabled'] = 'zlib enabled';
 
 
 $string['caching'] = 'Caching';
diff --git a/lang/en/backup.php b/lang/en/backup.php
index 18a34ff3719..fbc4bc3f226 100644
--- a/lang/en/backup.php
+++ b/lang/en/backup.php
@@ -117,6 +117,7 @@ $string['errorminbackup20version'] = 'This backup file has been created with one
 $string['errorrestorefrontpage'] = 'Restoring over front page is not allowed.';
 $string['errorinvalidformat'] = 'Unknown backup format';
 $string['errorinvalidformatinfo'] = 'The selected file is not a valid Moodle backup file and can\'t be restored.';
+$string['errortgznozlib'] = 'The selected file is in the new backup format and cannot be restored because the zlib PHP extension is not available on this system.';
 $string['executionsuccess'] = 'The backup file was successfully created.';
 $string['filename'] = 'Filename';
 $string['filealiasesrestorefailures'] = 'Aliases restore failures';
diff --git a/lib/filestorage/mbz_packer.php b/lib/filestorage/mbz_packer.php
index e149e35b284..c4c08e20f95 100644
--- a/lib/filestorage/mbz_packer.php
+++ b/lib/filestorage/mbz_packer.php
@@ -137,14 +137,16 @@ class mbz_packer extends file_packer {
     }
 
     /**
-     * Selects appropriate packer for new archive depending on system option.
+     * Selects appropriate packer for new archive depending on system option
+     * and whether required extension is available.
      *
      * @return file_packer Suitable packer
      */
     protected function get_packer_for_archive_operation() {
         global $CFG;
+        require_once($CFG->dirroot . '/lib/filestorage/tgz_packer.php');
 
-        if ($CFG->enabletgzbackups) {
+        if ($CFG->enabletgzbackups && tgz_packer::has_required_extension()) {
             return get_file_packer('application/x-gzip');
         } else {
             return get_file_packer('application/zip');
@@ -156,13 +158,18 @@ class mbz_packer extends file_packer {
      *
      * @param string|stored_file $archivefile full pathname of zip file or stored_file instance
      * @return file_packer Suitable packer
+     * @throws moodle_exception If the file cannot be restored because of missing zlib
      */
     protected function get_packer_for_read_operation($archivefile) {
         global $CFG;
         require_once($CFG->dirroot . '/lib/filestorage/tgz_packer.php');
 
         if (tgz_packer::is_tgz_file($archivefile)) {
-            return get_file_packer('application/x-gzip');
+            if (tgz_packer::has_required_extension()) {
+                return get_file_packer('application/x-gzip');
+            } else {
+                throw new moodle_exception('errortgznozlib', 'backup');
+            }
         } else {
             return get_file_packer('application/zip');
         }
diff --git a/lib/filestorage/tests/mbz_packer_test.php b/lib/filestorage/tests/mbz_packer_test.php
index cdb7bef92fb..b232e4f94e4 100644
--- a/lib/filestorage/tests/mbz_packer_test.php
+++ b/lib/filestorage/tests/mbz_packer_test.php
@@ -35,6 +35,11 @@ class core_files_mbz_packer_testcase extends advanced_testcase {
 
         // Get backup packer.
         $packer = get_file_packer('application/vnd.moodle.backup');
+        require_once($CFG->dirroot . '/lib/filestorage/tgz_packer.php');
+        if (!tgz_packer::has_required_extension()) {
+            $this->markTestSkipped('zlib not available');
+            return;
+        }
 
         // Set up basic archive contents.
         $files = array('1.txt' => array('frog'));
diff --git a/lib/filestorage/tests/tgz_packer_test.php b/lib/filestorage/tests/tgz_packer_test.php
index d61d264d2d2..d495ec82fd3 100644
--- a/lib/filestorage/tests/tgz_packer_test.php
+++ b/lib/filestorage/tests/tgz_packer_test.php
@@ -114,6 +114,9 @@ class core_files_tgz_packer_testcase extends advanced_testcase implements file_p
     public function test_to_normal_files() {
         global $CFG;
         $packer = get_file_packer('application/x-gzip');
+        if (self::skip_because_missing_zlib()) {
+            return;
+        }
 
         // Archive files.
         $files = $this->prepare_file_list();
@@ -154,6 +157,9 @@ class core_files_tgz_packer_testcase extends advanced_testcase implements file_p
      */
     public function test_to_stored_files() {
         global $CFG;
+        if (self::skip_because_missing_zlib()) {
+            return;
+        }
         $packer = get_file_packer('application/x-gzip');
 
         // Archive files.
@@ -220,6 +226,9 @@ class core_files_tgz_packer_testcase extends advanced_testcase implements file_p
      */
     public function test_only_specified_files() {
         global $CFG;
+        if (self::skip_because_missing_zlib()) {
+            return;
+        }
         $packer = get_file_packer('application/x-gzip');
 
         // Archive files.
@@ -252,6 +261,9 @@ class core_files_tgz_packer_testcase extends advanced_testcase implements file_p
      */
     public function test_file_progress() {
         global $CFG;
+        if (self::skip_because_missing_zlib()) {
+            return;
+        }
 
         // Set up.
         $filelist = $this->prepare_file_list();
@@ -309,6 +321,9 @@ class core_files_tgz_packer_testcase extends advanced_testcase implements file_p
      */
     public function test_list_files() {
         global $CFG;
+        if (self::skip_because_missing_zlib()) {
+            return;
+        }
 
         // Set up.
         $filelist = $this->prepare_file_list();
@@ -376,6 +391,9 @@ class core_files_tgz_packer_testcase extends advanced_testcase implements file_p
 
     public function test_is_tgz_file() {
         global $CFG;
+        if (self::skip_because_missing_zlib()) {
+            return;
+        }
 
         // Set up.
         $filelist = $this->prepare_file_list();
@@ -428,4 +446,19 @@ class core_files_tgz_packer_testcase extends advanced_testcase implements file_p
     public function progress($progress = file_progress::INDETERMINATE, $max = file_progress::INDETERMINATE) {
         $this->progress[] = array($progress, $max);
     }
+
+    /**
+     * Checks if zlib is available. If not, marks current test as skipped.
+     *
+     * @return bool True if text should be skipped
+     */
+    protected function skip_because_missing_zlib() {
+        global $CFG;
+        require_once($CFG->dirroot . '/lib/filestorage/tgz_packer.php');
+        if (!tgz_packer::has_required_extension()) {
+            $this->markTestSkipped('zlib not available');
+            return true;
+        }
+        return false;
+    }
 }
diff --git a/lib/filestorage/tgz_packer.php b/lib/filestorage/tgz_packer.php
index bfa459d7a7b..c47662aaa05 100644
--- a/lib/filestorage/tgz_packer.php
+++ b/lib/filestorage/tgz_packer.php
@@ -695,6 +695,16 @@ class tgz_packer extends file_packer {
         fclose($fp);
         return ($firstbytes[0] == "\x1f" && $firstbytes[1] == "\x8b");
     }
+
+    /**
+     * The zlib extension is required for this packer to work. This is a single
+     * location for the code to check whether the extension is available.
+     *
+     * @return bool True if the extension is available OK
+     */
+    public static function has_required_extension() {
+        return extension_loaded('zlib');
+    }
 }
 
 
diff --git a/mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php b/mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php
index a5046043d0c..088fd9f94dc 100644
--- a/mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php
+++ b/mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php
@@ -89,5 +89,4 @@ $string['unsavedchanges'] = 'Unsaved changes';
 $string['viewfeedbackonline'] = 'View annotated pdf...';
 $string['white'] = 'White';
 $string['yellow'] = 'Yellow';
-$string['zlibenabled'] = 'zlib enabled';
 $string['zlibnotavailable'] = 'Php extension "zlib" is not available. The annotate PDF feature relies on this php extension and will be disabled until zlib is installed and enabled.';
diff --git a/mod/assign/feedback/editpdf/settings.php b/mod/assign/feedback/editpdf/settings.php
index 10493d0a856..783126230f8 100644
--- a/mod/assign/feedback/editpdf/settings.php
+++ b/mod/assign/feedback/editpdf/settings.php
@@ -40,7 +40,7 @@ $settings->add(new admin_setting_configexecutable('assignfeedback_editpdf/gspath
                                                   '/usr/bin/gs'));
 
 $setting = new admin_setting_php_extension_enabled('assignfeedback_editpdf/zlibenabled',
-                                                   get_string('zlibenabled', 'assignfeedback_editpdf'),
+                                                   get_string('zlibenabled', 'admin'),
                                                    get_string('zlibnotavailable', 'assignfeedback_editpdf'),
                                                    'zlib');