diff --git a/src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd b/src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd
index 403119842e..0a7a56f675 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd
+++ b/src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd
@@ -578,7 +578,7 @@
 
     <xsd:complexType name="mailer_envelope">
         <xsd:sequence>
-            <xsd:element name="sender" type="xsd:string" />
+            <xsd:element name="sender" type="xsd:string" minOccurs="0" maxOccurs="1" />
             <xsd:element name="recipients" type="xsd:string" minOccurs="0" maxOccurs="unbounded" />
         </xsd:sequence>
     </xsd:complexType>