diff --git a/src/pg.ml b/src/pg.ml
index 58740201..ee470c43 100644
--- a/src/pg.ml
+++ b/src/pg.ml
@@ -349,7 +349,7 @@ let insert_wire_fee =
     Conn.exec insert_wire_fee
       (wire_method, fee_start, fee_end, wire_fee, closing_fee, master_sig_wire)
 
-(* TODO return type *)
+(* TODO return type, use AggregateTransferFee.t *)
 let get_wire_fees_by_time =
   let lookup_wire_fee_by_time =
     Caqti_type.(t3 wire_method time time ->* t2 amount amount)