diff --git a/admin/include/updates.class.php b/admin/include/updates.class.php
index 9b837e90b..934fde731 100644
--- a/admin/include/updates.class.php
+++ b/admin/include/updates.class.php
@@ -545,9 +545,14 @@ class updates
             self::process_obsolete_list($obsolete_list);
             deltree(PHPWG_ROOT_PATH.$conf['data_location'].'update');
             invalidate_user_cache(true);
-            $template->delete_compiled_templates();
             if ($step == 2)
             {
+              // only delete compiled templates on minor update. Doing this on
+              // a major update might even encounter fatal error if Smarty
+              // changes. Anyway, a compiled template purge will be performed
+              // by upgrade.php
+              $template->delete_compiled_templates();
+
               $page['infos'][] = l10n('Update Complete');
               $page['infos'][] = $upgrade_to;
               $step = -1;
diff --git a/include/smarty/libs/sysplugins/smarty_internal_undefined.php b/include/smarty/libs/sysplugins/smarty_internal_undefined.php
index 7df0acc2d..635b4818b 100644
--- a/include/smarty/libs/sysplugins/smarty_internal_undefined.php
+++ b/include/smarty/libs/sysplugins/smarty_internal_undefined.php
@@ -61,6 +61,15 @@ class Smarty_Internal_Undefined
         if (isset($this->class)) {
             throw new SmartyException("undefined extension class '{$this->class}'");
         } else {
+            // Piwigo specifics - starts here
+            // when updating from Piwigo 11 to 12, we try to delete compiled templates and there is a mix old and new Smarty files, resulting in a:
+            // Fatal error: Uncaught --> Smarty: Smarty->_clearTemplateCache() undefined method
+            // indeed this method does not exist in Smarty 3.1.29 (Piwigo 11) but exists in Smarty 3.1.39 (Piwigo 12)
+            if ('_clearTemplateCache' == $name)
+            {
+                return;
+            }
+            // Piwigo specifics - stops here
             throw new SmartyException(get_class($args[ 0 ]) . "->{$name}() undefined method");
         }
     }