diff --git a/htdocs/adherents/class/adherent_type.class.php b/htdocs/adherents/class/adherent_type.class.php
index 90b34e604be..cdf021cfa68 100644
--- a/htdocs/adherents/class/adherent_type.class.php
+++ b/htdocs/adherents/class/adherent_type.class.php
@@ -90,7 +90,7 @@ class AdherentType extends CommonObject
 	public $subscription;
 
 	/**
-	 * @var float amount for subscription
+	 * @var float|string 	Amount for subscription (null or '' means not defined)
 	 */
 	public $amount;