diff --git a/config.php b/config.php
index 3624d71..108d0b2 100644
--- a/config.php
+++ b/config.php
@@ -66,7 +66,18 @@ class config
     if ($rc !== 1)
       throw new Exception ("Error in configuration file");
     if (array_key_exists ($param, $conf))
+    {
+      if (! is_array ($conf[$param]))
+        return $conf[$param];
+      // if the configuration is an array, check if all the keys are defined
+      // or use the default
+      foreach ($this->default[$param] as $key=>$val)
+      {
+        if (! isset ($conf[$param][$key]))
+          $conf[$param][$key] = $val;
+      }
       return $conf[$param];
+    }
     return $this->default[$param];
   }