diff --git a/lib/irc/mode.ml b/lib/irc/mode.ml
index 1dd05fe..71a80b3 100644
--- a/lib/irc/mode.ml
+++ b/lib/irc/mode.ml
@@ -145,7 +145,7 @@ module Parse = struct
     in
     loop `none init 0
 
-  let take = function
+  let take_string = function
     | [] -> fail "expected argument"
     | x :: xs -> x, xs
 
@@ -154,6 +154,15 @@ module Parse = struct
     | x :: xs -> try int_of_string x, xs
       with Invalid_argument _ -> fail "invalid integer"
 
+  let is_valid_key = function
+    | "" | "*" -> false
+    | _ -> true
+
+  let take_key = function
+    | [] -> fail "expected argument"
+    | x :: xs when is_valid_key x -> x, xs
+    | _ -> fail "invalid key"
+
   type user_modes = Set.change
 
   let user_modes str =
@@ -190,12 +199,12 @@ module Parse = struct
       args, modes
     | `k ->
       (* type B *)
-      let key, args = take args in
+      let key, args = take_key args in
       let chan_key = Some (`set key) in
       args, { modes with chan_key }
     | (`o | `v) as priv ->
       (* type B *)
-      let nick, args = take args in
+      let nick, args = take_string args in
       let chan_privs = (`add, priv, nick) :: modes.chan_privs in
       args, { modes with chan_privs }
     | `l ->
@@ -218,7 +227,7 @@ module Parse = struct
       args, modes
     | `k ->
       (* type B *)
-      let _key, args = take args in
+      let _key, args = take_string args in
       let chan_key = Some `unset in
       args, { modes with chan_key }
     | `l ->
@@ -227,7 +236,7 @@ module Parse = struct
       args, { modes with chan_limit }
     | (`o | `v) as priv ->
       (* type B *)
-      let nick, args = take args in
+      let nick, args = take_string args in
       let chan_privs = (`rem, priv, nick) :: modes.chan_privs in
       args, { modes with chan_privs }
     | #chan_d as m ->