diff --git a/src/channels.rs b/src/channels.rs
index e856862..18f4fec 100644
--- a/src/channels.rs
+++ b/src/channels.rs
@@ -1455,10 +1455,10 @@ pub fn normalize_ban_mask(m: &str) -> String {
     let b = m.as_bytes();
     if b.len() >= 2 && b[1] == b':' && (b[0] as char).is_ascii_alphabetic() {
         // These extbans carry a name / spec / channel / server, not a host mask,
-        // so they must not be host-normalised: g: (security group), y: (reputation
-        // score), r: (realname), j: (channel), s: (server name), G: (country),
-        // b: (banned-in-channel).
-        if matches!(b[0], b'g' | b'y' | b'r' | b'j' | b's' | b'G' | b'b') {
+        // so they must not be host-normalised: a: (account), g: (security group),
+        // y: (reputation score), r: (realname), j: (channel), s: (server name),
+        // G: (country), b: (banned-in-channel).
+        if matches!(b[0], b'a' | b'g' | b'y' | b'r' | b'j' | b's' | b'G' | b'b') {
             return m.to_string();
         }
         return format!("{}:{}", &m[..1], normalize_mask(&m[2..]));
@@ -1470,6 +1470,14 @@ pub fn normalize_ban_mask(m: &str) -> String {
 mod tests {
     use super::*;
 
+    #[test]
+    fn account_extban_mask_is_left_verbatim() {
+        // a: carries an account name, not a host mask — must not gain !*@*
+        assert_eq!(normalize_ban_mask("a:someacct*"), "a:someacct*");
+        // a bare nick is still host-normalised the usual way
+        assert!(normalize_ban_mask("bob").contains('@'));
+    }
+
     #[test]
     fn member_rank_and_prefix_char_take_the_highest() {
         let mut m = Member::default();