diff --git a/grc/ieee802_11_decode_mac.xml b/grc/ieee802_11_decode_mac.xml
index d0fc461..fe527db 100644
--- a/grc/ieee802_11_decode_mac.xml
+++ b/grc/ieee802_11_decode_mac.xml
@@ -48,6 +48,7 @@
 	<source>
 		<name>out</name>
 		<type>message</type>
+		<optional>1</optional>
 	</source>
 
 </block>