diff --git a/modules/chanserv/src/mode.rs b/modules/chanserv/src/mode.rs
index 11290a5..8b8f718 100644
--- a/modules/chanserv/src/mode.rs
+++ b/modules/chanserv/src/mode.rs
@@ -1,7 +1,9 @@
 use echo_api::Store;
 use echo_api::{Sender, ServiceCtx};
 
-// MODE <#channel> <modes>: the founder sets channel modes via ChanServ.
+// MODE <#channel> <modes>: the founder sets channel modes via ChanServ. Extban
+// arguments on the ban-family list modes (+b/+e/+I) are held to the same
+// `[extban] enabled` policy as AKICK; everything else passes to the ircd as-is.
 pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db: &mut dyn Store) {
     let Some(&chan) = args.get(1) else {
         ctx.notice(me, from.uid, "Syntax: MODE <#channel> <modes>, e.g. MODE #chan +nt");
@@ -22,7 +24,71 @@ pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db:
         ctx.notice(me, from.uid, format!("Only \x02{chan}\x02's founder can change its modes."));
         return;
     }
+    // Reject an extban the network has turned off, before relaying anything.
+    for mask in ban_masks(&args[2..]) {
+        let core = mask.strip_prefix('!').unwrap_or(mask); // extbans may be inverted
+        if let echo_api::AkickMask::Ext(eb, _) = echo_api::AkickMask::parse(core) {
+            if !db.extban_enabled(eb.name) {
+                ctx.notice(me, from.uid, format!("The \x02{}\x02 extban isn't enabled on this network.", eb.name));
+                return;
+            }
+        }
+    }
     let modes = args[2..].join(" ");
     ctx.channel_mode(me, chan, &modes);
     ctx.notice(me, from.uid, format!("Set \x02{modes}\x02 on \x02{chan}\x02."));
 }
+
+// Whether a channel mode consumes a parameter. List modes (b/e/I) and prefix
+// modes (qaohv) take one on both + and -, as does the key (k); the type-C modes
+// (limit, redirect, flood) only when added. Params are paired in IRC MODE order,
+// so every param-taking mode must be accounted for to find the ban masks.
+fn mode_takes_param(c: char, adding: bool) -> bool {
+    match c {
+        'b' | 'e' | 'I' | 'q' | 'a' | 'o' | 'h' | 'v' | 'k' => true,
+        'l' | 'L' | 'f' | 'j' | 'J' => adding,
+        _ => false,
+    }
+}
+
+// The parameters attached to +b/-b/+e/-e/+I/-I in a `<modes> [params...]` change.
+fn ban_masks<'a>(tokens: &'a [&'a str]) -> Vec<&'a str> {
+    let modes = tokens.first().copied().unwrap_or("");
+    let mut params = tokens.iter().skip(1);
+    let mut adding = true;
+    let mut out = Vec::new();
+    for ch in modes.chars() {
+        match ch {
+            '+' => adding = true,
+            '-' => adding = false,
+            m if mode_takes_param(m, adding) => {
+                if let Some(&p) = params.next() {
+                    if matches!(m, 'b' | 'e' | 'I') {
+                        out.push(p);
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::ban_masks;
+
+    #[test]
+    fn ban_masks_pairs_params_in_mode_order() {
+        // A lone ban, and a ban after a prefix mode: the mask must pair to +b.
+        assert_eq!(ban_masks(&["+b", "account:x"]), ["account:x"]);
+        assert_eq!(ban_masks(&["+ob", "nick", "account:x"]), ["account:x"]);
+        // The key's value is not a ban mask even when it looks like an extban.
+        assert!(ban_masks(&["+k", "account:secret"]).is_empty());
+        // Exceptions and invex count; plain flag modes carry nothing.
+        assert_eq!(ban_masks(&["+eI", "R:a", "r:b"]), ["R:a", "r:b"]);
+        assert!(ban_masks(&["+nt"]).is_empty());
+        // Removal still carries a mask.
+        assert_eq!(ban_masks(&["-b", "*!*@h"]), ["*!*@h"]);
+    }
+}