diff --git a/lib/irc/msg.ml b/lib/irc/msg.ml
index 37bf4c7..fd029eb 100644
--- a/lib/irc/msg.ml
+++ b/lib/irc/msg.ml
@@ -30,9 +30,12 @@ type t = {
   trailing : bool;
 } [@@deriving show { with_path = false }]
 
+let is_param_trailing p =
+  String.starts_with p ~prefix:":" || String.contains p ' '
+
 let rec is_params_trailing = function
   | [] -> false
-  | [tr] -> String.contains tr ' '
+  | [p] -> is_param_trailing p
   | _ :: tl -> is_params_trailing tl
 
 let make ?(prefix = No_prefix) ?(always_trailing = false) command params =
@@ -48,12 +51,12 @@ let write buf t =
   Buffer.add_string buf t.command;
   let rec add_params = function
     | [] -> ()
-    | [tr] when t.trailing ->
+    | [p] when t.trailing ->
       Buffer.add_string buf " :";
-      Buffer.add_string buf tr
-    | hd::tl ->
+      Buffer.add_string buf p
+    | p::tl ->
       Buffer.add_char buf ' ';
-      Buffer.add_string buf hd;
+      Buffer.add_string buf p;
       add_params tl
   in
   add_params t.params;
@@ -168,6 +171,9 @@ let%expect_test _ =
   make "NICK" ["tali"] |> print_msg_nl;
   [%expect {| "NICK tali\r\n" |}];
 
+  make "NICK" [":)"] |> print_msg_nl;
+  [%expect {| "NICK ::)\r\n" |}];
+
   make "USER" ["milo"; "0"; "*"; "milo"] ~always_trailing:true |> print_msg_nl;
   [%expect {| "USER milo 0 * :milo\r\n" |}];