diff --git a/api/kessel/relations/v1beta1/common.proto b/api/kessel/relations/v1beta1/common.proto
index ef539f6..ceabe7d 100644
--- a/api/kessel/relations/v1beta1/common.proto
+++ b/api/kessel/relations/v1beta1/common.proto
@@ -46,6 +46,6 @@ message ObjectReference {
 }
 
 message ObjectType {
-	string namespace = 1 [(validate.rules).string.min_len = 1];
+	optional string namespace = 1 [(validate.rules).string.min_len = 1];
 	string name = 2 [(validate.rules).string.min_len = 1];
 }