diff --git a/program/lib/Roundcube/db/pgsql.php b/program/lib/Roundcube/db/pgsql.php
index 13f5724437a..9195998f1a6 100644
--- a/program/lib/Roundcube/db/pgsql.php
+++ b/program/lib/Roundcube/db/pgsql.php
@@ -173,7 +173,10 @@ public function get_variable($varname, $default = null)
             return rcube::get_instance()->config->get('db_' . $varname, $default);
         }
 
-        $this->variables[$varname] = rcube::get_instance()->config->get('db_' . $varname);
+        $cfgval = rcube::get_instance()->config->get('db_' . $varname);
+        if (isset($cfgval)) {
+            return $cfgval;
+        }
 
         if (!isset($this->variables)) {
             $this->variables = [];