diff --git a/proto/invitations/invitations.proto b/proto/invitations/invitations.proto
index 83c17fb6597d0103fcbbfc11bdfbcd8e7e3b42e9..48def3af93dc97fddc1f765dcb217920df166699 100644
--- a/proto/invitations/invitations.proto
+++ b/proto/invitations/invitations.proto
@@ -11,7 +11,7 @@ package content.invitations;
 
 message Invitation {
   string id = 1;
-  string email = 2;
+  optional string email = 2;
   string org_id = 3;
   string space_id = 4;
   string owner_id = 5;