diff --git a/admin/configuration.php b/admin/configuration.php
index 32ff2d9b6..4d04f8a98 100644
--- a/admin/configuration.php
+++ b/admin/configuration.php
@@ -355,10 +355,12 @@ WHERE param = \''.$row['param'].'\'
 // restore default derivatives settings
 if ('sizes' == $page['section'] and isset($_GET['action']) and 'restore_settings' == $_GET['action'])
 {
-  ImageStdParams::set_and_save( ImageStdParams::get_default_sizes() );
-  pwg_query('DELETE FROM '.CONFIG_TABLE.' WHERE param = \'disabled_derivatives\'');
+  ImageStdParams::restore_default();
   clear_derivative_cache();
 
+  // reset conf
+  load_conf_from_db();
+
   $template->assign(
     array(
       'save_success' => l10n('Your configuration settings are saved'),
@@ -569,7 +571,7 @@ switch ($page['section'])
 
       // derivatives = multiple size
       $enabled = ImageStdParams::get_defined_type_map();
-      $disabled = @unserialize(@$conf['disabled_derivatives']);
+      $disabled = safe_unserialize(ImageStdParams::get_disabled_type_map());
       if ($disabled === false)
       {
         $disabled = array();
diff --git a/admin/include/configuration_sizes_process.inc.php b/admin/include/configuration_sizes_process.inc.php
index f79a7c975..9110c835e 100644
--- a/admin/include/configuration_sizes_process.inc.php
+++ b/admin/include/configuration_sizes_process.inc.php
@@ -134,7 +134,7 @@ if (count($errors) == 0)
   ImageStdParams::$quality = intval($_POST['resize_quality']);
 
   $enabled = ImageStdParams::get_defined_type_map();
-  $disabled = @unserialize( @$conf['disabled_derivatives'] );
+  $disabled = safe_unserialize(ImageStdParams::get_disabled_type_map());
   if ($disabled === false)
   {
     $disabled = array();
@@ -228,16 +228,7 @@ if (count($errors) == 0)
   }
 
   ImageStdParams::set_and_save($enabled_by);
-  if (count($disabled) == 0)
-  {
-    $query='DELETE FROM '.CONFIG_TABLE.' WHERE param = \'disabled_derivatives\'';
-    pwg_query($query);
-  }
-  else
-  {
-    conf_update_param('disabled_derivatives', addslashes(serialize($disabled)) );
-  }
-  $conf['disabled_derivatives'] = serialize($disabled);
+  ImageStdParams::set_and_save_disabled($disabled);
 
   if (count($changed_types))
   {
diff --git a/admin/include/functions_upload.inc.php b/admin/include/functions_upload.inc.php
index 1f0fa325b..1ffb18c0a 100644
--- a/admin/include/functions_upload.inc.php
+++ b/admin/include/functions_upload.inc.php
@@ -1105,7 +1105,7 @@ function get_optimal_dimensions_for_representative()
   global $conf;
 
   $enabled = ImageStdParams::get_defined_type_map();
-  $disabled = @unserialize(@$conf['disabled_derivatives']);
+  $disabled = safe_unserialize(ImageStdParams::get_disabled_type_map());
   if ($disabled === false)
   {
     $disabled = array();
diff --git a/include/derivative_std_params.inc.php b/include/derivative_std_params.inc.php
index b39428940..64bac673a 100644
--- a/include/derivative_std_params.inc.php
+++ b/include/derivative_std_params.inc.php
@@ -57,11 +57,15 @@ final class ImageStdParams
     IMG_SQUARE, IMG_THUMB, IMG_XXSMALL, IMG_XSMALL, IMG_SMALL,
     IMG_MEDIUM, IMG_LARGE, IMG_XLARGE, IMG_XXLARGE, IMG_3XLARGE, IMG_4XLARGE
     );
+  /** @var string[] */
+  private static $disabled_types_by_default = array(IMG_3XLARGE, IMG_4XLARGE);
   /** @var DerivativeParams[] */
   private static $all_type_map = array();
   /** @var DerivativeParams[] */
   private static $type_map = array();
   /** @var DerivativeParams[] */
+  private static $disabled_type_map = array();
+  /** @var DerivativeParams[] */
   private static $undefined_type_map = array();
   /** @var WatermarkParams */
   private static $watermark;
@@ -94,6 +98,18 @@ final class ImageStdParams
     return self::$type_map;
   }
 
+  /**
+   * @return DerivativeParams[]
+   */
+  static function get_disabled_type_map()
+  {
+    if (count(self::$disabled_type_map))
+    {
+      return self::$disabled_type_map;
+    }
+    return conf_get_param('disabled_derivatives', array());
+  }
+
   /**
    * @return DerivativeParams[]
    */
@@ -161,7 +177,8 @@ final class ImageStdParams
     else
     {
       self::$watermark = new WatermarkParams();
-      self::$type_map = self::get_default_sizes();
+      self::$type_map = self::get_enabled_default_sizes();
+      self::$disabled_type_map = self::get_disabled_default_sizes();
       self::save();
     }
     self::build_maps();
@@ -199,6 +216,39 @@ final class ImageStdParams
       'c' => self::$custom,
       ) );
     conf_update_param('derivatives', addslashes($ser) );
+
+    self::save_disabled();
+  }
+
+  /**
+   * Saves the disabled configuration in database.
+   */
+  static function save_disabled()
+  {
+    if (count(self::$disabled_type_map) > 0)
+    {
+      $disabled = addslashes(serialize(self::$disabled_type_map));
+      conf_update_param('disabled_derivatives', $disabled);
+    }
+    else
+    {
+      $query='DELETE FROM '.CONFIG_TABLE.' WHERE param = \'disabled_derivatives\'';
+      pwg_query($query);
+    }
+  }
+
+  static function set_and_save_disabled($map)
+  {
+    self::$disabled_type_map = $map;
+    self::save_disabled();
+  }
+
+  static function restore_default()
+  {
+    self::$type_map = self::get_enabled_default_sizes();
+    self::$disabled_type_map = self::get_disabled_default_sizes();
+    self::save();
+    self::build_maps();
   }
 
   /**
@@ -227,6 +277,29 @@ final class ImageStdParams
     return $arr;
   }
 
+  /**
+   * @return DerivativeParams[]
+   */
+  static function get_enabled_default_sizes()
+  {
+    $default_sizes = self::get_default_sizes();
+    foreach (self::$disabled_types_by_default as $type)
+    {
+      unset($default_sizes[$type]);
+    }
+    return $default_sizes;
+  }
+
+  /**
+   * @return DerivativeParams[]
+   */
+  static function get_disabled_default_sizes()
+  {
+    $all = self::get_default_sizes();
+    $disabled_sizes = array_intersect_key($all, array_flip(self::$disabled_types_by_default));
+    return $disabled_sizes;
+  }
+
   /**
    * Compute 'apply_watermark'
    *
diff --git a/install/db/177-database.php b/install/db/177-database.php
index 259c901f2..921d59108 100644
--- a/install/db/177-database.php
+++ b/install/db/177-database.php
@@ -11,54 +11,25 @@ if (!defined('PHPWG_ROOT_PATH'))
   die('Hacking attempt!');
 }
 
-global $conf;
+$upgrade_description = 'Add 3XL and 4XL sizes (disabled by default)';
+
 load_conf_from_db();
 
-$upgrade_description = 'Add 3XL and 4XL sizes';
-
-//Get predefined image sizes
-$derivatives = unserialize($conf['derivatives']);
-
 //get default sizes from derivative_std_params
 $default_sizes = ImageStdParams::get_default_sizes();
 
-//Get 3XL and 4XL from default values
-$default_derivative_3XL = $default_sizes['3xlarge'];
-$default_derivative_4XL = $default_sizes['4xlarge'];
+// set new derivatives to add
+$new_derivatives = array(IMG_3XLARGE, IMG_4XLARGE);
 
-//We need to make sure that a user hasn't redefined the XXL size bigger than the default 3XL
-//Get xxl size
-$xxl = $derivatives['d']['xxlarge'];
-$xxl_height = $xxl->sizing->ideal_size[0];
-$xxl_width = $xxl->sizing->ideal_size[1];
+// get current disabled derivative_std_params
+$disabled_derivatives = safe_unserialize(ImageStdParams::get_disabled_type_map());
 
-//get 3xl size
-$triple_xl_height = $default_sizes['3xlarge']->sizing->ideal_size[0];
-$triple_xl_width = $default_sizes['3xlarge']->sizing->ideal_size[1];
+// get the new derivative_std_params and merge with current disabled derivative_std_params
+$new_disabled_derivatives = array_intersect_key($default_sizes, array_flip($new_derivatives));
+$disabled = array_merge($disabled_derivatives, $new_disabled_derivatives);
 
-//Get 4xl size
-$quad_xl_height = $default_sizes['3xlarge']->sizing->ideal_size[0];
-$quad_xl_width = $default_sizes['3xlarge']->sizing->ideal_size[1];
-
-//Set 3XL and 4xl size to be bigger than XXL if needed
-if ($triple_xl_height < $xxl_height or $triple_xl_width < $xxl_width)
-{
-  $new_3xl_height = ceil($xxl_height*1.5);
-  $new_3xl_width = ceil($xxl_width*1.5);
-
-  $default_sizes['3xlarge']->sizing->ideal_size[0] = $new_3xl_height;
-  $default_sizes['3xlarge']->sizing->ideal_size[1] = $new_3xl_width;
-
-  $default_sizes['4xlarge']->sizing->ideal_size[0] = ceil($new_3xl_width*1.5);
-  $default_sizes['4xlarge']->sizing->ideal_size[1] = ceil($new_3xl_width*1.5);
-}
-
-//Add new 3xl and 4xl to derivatives sizes config
-$derivatives['d'][IMG_3XLARGE] = $default_sizes['3xlarge'];
-$derivatives['d'][IMG_4XLARGE] = $default_sizes['4xlarge'];
-
-// Save derivative new settings
-ImageStdParams::set_and_save($derivatives['d']);
+// set and set new derivative_std_params in disabled list
+ImageStdParams::set_and_save_disabled($disabled);
 
 echo "\n".$upgrade_description."\n";
 ?>
\ No newline at end of file