diff --git a/src/routes/channels/message_send.rs b/src/routes/channels/message_send.rs
index f3bbe03d..d83e9a38 100644
--- a/src/routes/channels/message_send.rs
+++ b/src/routes/channels/message_send.rs
@@ -30,7 +30,8 @@ pub struct Data {
 }
 
 lazy_static! {
-    static ref RE_ULID: Regex = Regex::new(r"<@([0-9A-Z]{26})>").unwrap();
+    // ignoring I L O and U is intentional
+    static ref RE_ULID: Regex = Regex::new(r"<@([0-9A-HJKMNPQRSTVWXYZ]{26})>").unwrap();
 }
 
 #[post("/<target>/messages", data = "<message>")]