diff --git a/lib/irc/mode.ml b/lib/irc/mode.ml
index fc51241..cd6003b 100644
--- a/lib/irc/mode.ml
+++ b/lib/irc/mode.ml
@@ -1,89 +1,70 @@
-type t = int
+type user = [`i | `o | `w]
+type chan_a = [`b]
+type chan_b = [`k | `o | `v]
+type chan_c = [`l]
+type chan_d = [`i | `m | `s | `t | `n]
+type chan = [chan_a | chan_b | chan_c | chan_d]
+type t = [user | chan]
 
-let _o = 1
-let _a = 2
-let _w = 4
-let _i = 8
-let _r = 16
-let _O = 32
-let _s = 64
+let to_string = function
+  | `b -> "b"
+  | `i -> "i"
+  | `k -> "k"
+  | `l -> "l"
+  | `m -> "m"
+  | `n -> "n"
+  | `o -> "o"
+  | `s -> "s"
+  | `t -> "t"
+  | `v -> "v"
+  | `w -> "w"
 
-let all ts = List.fold_left (lor) 0 ts
-let filter t u = t land u
+let to_char x = (to_string x).[0]
+let pp ppf x = Format.pp_print_string ppf (to_string x)
 
-let of_bitmask_string ?(allowed = 12) s =
-  (* This parameter is a bitmask, with only 2 bits having any signification: if the bit 2
-     is set, the user mode 'w' will be set and if the bit 3 is set, the user mode 'i' will
-     be set. *)
-  try filter (int_of_string s) allowed
-  with Failure _ -> 0
+let of_char_user = function
+  | 'i' -> `i
+  | 'o' -> `o
+  | 'w' -> `w
+  | _ -> invalid_arg "Mode.of_char_user"
 
-let of_char = function
-  | 'o' -> _o
-  | 'a' -> _a
-  | 'w' -> _w
-  | 'i' -> _i
-  | 'r' -> _r
-  | 'O' -> _O
-  | 's' -> _s
-  | _ -> 0
+let of_char_chan = function
+  | 'b' -> `b
+  | 'i' -> `i
+  | 'k' -> `k
+  | 'l' -> `l
+  | 'm' -> `m
+  | 'n' -> `n
+  | 'o' -> `o
+  | 's' -> `s
+  | 't' -> `t
+  | 'v' -> `v
+  | _ -> invalid_arg "Mode.of_char_chan"
 
-let pp ppf t =
-  let f ch =
-    if t land (of_char ch) <> 0 then
-      Format.pp_print_char ppf ch
-  in
-  String.iter f "aiwroOs"
-
-let rec of_string_rec s acc i =
-  if i >= String.length s then
-    acc
-  else
-    of_string_rec s (acc lor of_char s.[i]) (i + 1)
-
-let of_string s =
-  of_string_rec s 0 0
-
-type diff = int
-
-let pp_diff ppf d =
-  if d < 0 then
-    (Format.pp_print_string ppf "-"; pp ppf (-d))
-  else
-    (Format.pp_print_string ppf "+"; pp ppf d)
-
-let ( ~+ ) m = Int.abs m
-let ( ~- ) m = Int.neg (~+ m)
-
-let ( ^ ) t d =
-  if d < 0 then
-    Int.logand (Int.neg d |> Int.lognot) t
-  else
-    Int.logor d t
-
-let diff_of_string s =
-  if String.starts_with s ~prefix:"-" then
-    - of_string_rec s 0 1
-  else
-    + of_string s
-
-;;
+let[@warning "+8"] _check_exhaustive (x : chan) =
+  match x with
+  | #chan_a -> ()
+  | #chan_b -> ()
+  | #chan_c -> ()
+  | #chan_d -> ()
 
 let%expect_test _ =
-  let print_mode_nl m =
-    Format.kasprintf print_string "%a\n" pp m
+  let roundtrip of_char_x m =
+    match of_char_x (to_char m) with
+    | m' when m = m' -> ()
+    | m' -> Printf.printf "fail:%s!=%s\n" (to_string m) (to_string m')
+    | exception Invalid_argument _ -> Printf.printf "error:%s\n" (to_string m)
   in
+  let roundtrip_user m = roundtrip of_char_user m in
+  let roundtrip_chan m = roundtrip of_char_chan m in
 
-  print_mode_nl (_O); [%expect {| O |}];
-  print_mode_nl (all [_o; _a]); [%expect {| ao |}];
-  print_mode_nl (all [_i; _w; _i]); [%expect {| iw |}];
-  print_mode_nl (all [_o; _a]); [%expect {| ao |}];
-  print_mode_nl (all [_o; _a] ^ +_w); [%expect {| awo |}];
-  print_mode_nl (all [_o; _a; _i] ^ -_o); [%expect {| ai |}];
-
-  print_mode_nl (of_string "awrO"); [%expect {| awrO |}];
-  print_mode_nl (of_string "is"); [%expect {| is |}];
-  print_mode_nl (of_bitmask_string "0"); [%expect {| |}];
-  print_mode_nl (of_bitmask_string "4"); [%expect {| w |}];
-  print_mode_nl (of_bitmask_string "8"); [%expect {| i |}];
-  print_mode_nl (of_bitmask_string "12"); [%expect {| iw |}];
+  roundtrip_user `i;
+  roundtrip_user `w;
+  roundtrip_chan `i;
+  roundtrip_chan `k;
+  roundtrip_chan `l;
+  roundtrip_chan `m;
+  roundtrip_chan `n;
+  roundtrip_chan `o;
+  roundtrip_chan `s;
+  roundtrip_chan `t;
diff --git a/lib/irc/mode.mli b/lib/irc/mode.mli
index c4c2c55..75998d3 100644
--- a/lib/irc/mode.mli
+++ b/lib/irc/mode.mli
@@ -1,40 +1,38 @@
-type t
+(*
+   User Modes:
+       +i  Invisible User Mode
+       +o  Oper User Mode
+       +w  WALLOPS User Mode
 
-val pp : Format.formatter -> t -> unit
+   Channel Modes:
+     Type A:
+       +b  Ban Channel Mode
 
-val _a : t
-(** a - user is flagged as away **)
+     Type B:
+       +k  Key Channel Mode
+       +o  Operator Channel Membership Prefix (@)
+       +v  Voice Channel Membership Prefix (+)
 
-val _i : t
-(** i - marks a users as invisible **)
+     Type C:
+       +l  Client Limit Channel Mode
 
-val _w : t
-(** w - user receives wallops **)
+     Type D:
+       +i  Invite-Only Channel Mode
+       +m  Moderated Channel Mode
+       +s  Secret Channel Mode
+       +t  Protected Topic Channel Mode
+       +n  No External Messages Mode
+ *)
 
-val _r : t
-(** r - restricted user connection **)
+type user = [`i | `o | `w]
+type chan_a = [`b]
+type chan_b = [`k | `o | `v]
+type chan_c = [`l]
+type chan_d = [`i | `m | `s | `t | `n]
+type chan = [chan_a | chan_b | chan_c | chan_d]
+type t = [user | chan]
 
-val _o : t
-(** o - operator flag **)
-
-val _O : t
-(** O - local operator flag **)
-
-val _s : t
-(** s - marks a user for receipt of server notices **)
-
-val all : t list -> t
-val filter : t -> t -> t
-
-val of_char : char -> t
-val of_string : string -> t
-val of_bitmask_string : ?allowed:t -> string -> t
-
-type diff
-
-val pp_diff : Format.formatter -> t -> unit
-
-val ( ~+ ) : t -> diff
-val ( ~- ) : t -> diff
-val ( ^ ) : t -> diff -> t
-val diff_of_string : string -> t
+val pp : Format.formatter -> [< t] -> unit
+val to_char : [< t] -> char
+val of_char_user : char -> [> user]
+val of_char_chan : char -> [> chan]