diff --git a/src/mode.rs b/src/mode.rs
index af1ebb5..99dbf61 100644
--- a/src/mode.rs
+++ b/src/mode.rs
@@ -158,10 +158,25 @@ impl ChanMode for Prefix {
                 return Applied::No;
             }
         };
-        // must out-rank (or match) both the prefix being set and the target's
-        // current top rank — no de-opping someone above you.
+        // customprefix depriv=no: a member may not remove this prefix from themselves
+        if !adding && tuid == uid && !crate::modules::customprefix::can_depriv(self.ch) {
+            s.numeric(
+                uid,
+                ERR_CHANOPRIVSNEEDED,
+                &format!("{chan} :You may not remove +{} from yourself", self.ch),
+            );
+            return Applied::No;
+        }
+        // must out-rank (or match) both the rank needed to set/unset this prefix
+        // (customprefix ranktoset/ranktounset, default the prefix's own rank) and the
+        // target's current top rank — no de-opping someone above you.
+        let needed = if adding {
+            crate::modules::customprefix::rank_to_set(self.ch).unwrap_or(self.rank)
+        } else {
+            crate::modules::customprefix::rank_to_unset(self.ch).unwrap_or(self.rank)
+        };
         let src = s.rank(uid, key);
-        if src < self.rank || src < target_rank {
+        if src < needed || src < target_rank {
             s.numeric(
                 uid,
                 ERR_CHANOPRIVSNEEDED,
diff --git a/src/modules/customprefix.rs b/src/modules/customprefix.rs
index 928a9ae..ba95918 100644
--- a/src/modules/customprefix.rs
+++ b/src/modules/customprefix.rs
@@ -1,15 +1,22 @@
-//! customprefix — override the *symbol* (sigil) of the channel prefix tiers from
-//! config, e.g. show `!` for op instead of `@`. One line per tier:
+//! customprefix — reconfigure the channel prefix tiers from config, like InspIRCd's
+//! m_customprefix does for existing prefixes (`change="yes"`). One line per tier:
 //!
 //! ```text
-//! customprefix = op *          # ops show as *nick, PREFIX advertises it too
+//! customprefix = op * ranktoset=admin ranktounset=admin depriv=no
 //! customprefix = voice -
 //! ```
 //!
-//! Tiers: `oper founder admin op halfop voice`. Only the displayed symbol changes —
-//! the mode letters (`yqaohv`) and ranks stay fixed, so NAMES/WHO, ISUPPORT PREFIX
-//! and the S2S FJOIN burst stay consistent (a linked network must share this config,
-//! as with InspIRCd). Loaded once at boot; unset tiers keep their default sigil.
+//! Tiers: `oper founder admin op halfop voice`. Knobs:
+//!   * a bare token = the displayed sigil (e.g. `*`)
+//!   * `ranktoset=<rank>`   min rank to grant this prefix (default: the prefix's rank)
+//!   * `ranktounset=<rank>` min rank to revoke it (default: ranktoset)
+//!   * `depriv=no`          members may not remove this prefix from themselves
+//!
+//! A `<rank>` is a number (1–6) or a tier name (`op`, `admin`, …). Only the display
+//! and set/unset policy change — the mode letters (`yqaohv`) and ranks stay fixed, so
+//! NAMES/WHO, ISUPPORT PREFIX and the S2S FJOIN burst stay consistent (a linked
+//! network must share this config). Adding brand-new tiers with new letters/ranks
+//! would need a data-driven prefix engine and isn't supported. Loaded once at boot.
 
 use std::sync::OnceLock;
 
@@ -18,37 +25,68 @@ use crate::server::Server;
 const TIER_NAMES: [&str; 6] = ["oper", "founder", "admin", "op", "halfop", "voice"];
 const LETTERS: [char; 6] = ['y', 'q', 'a', 'o', 'h', 'v'];
 const DEFAULT_SIGILS: [&str; 6] = ["!", "~", "&", "@", "%", "+"];
+const RANKS: [u8; 6] = [6, 5, 4, 3, 2, 1]; // oper..voice
 
-/// The configured sigils, indexed by tier. Being a `static` its `String`s live for
-/// the program, so `sigil()` can hand out `&'static str` without leaking.
-static SIGILS: OnceLock<[String; 6]> = OnceLock::new();
+struct PrefixCfg {
+    sigils: [String; 6],
+    ranktoset: [Option<u8>; 6],
+    ranktounset: [Option<u8>; 6],
+    depriv: [bool; 6],
+}
+
+static CFG: OnceLock<PrefixCfg> = OnceLock::new();
+
+/// Parse a rank: a number (1–6) or a tier name.
+fn parse_rank(v: &str) -> Option<u8> {
+    if let Ok(n) = v.parse::<u8>() {
+        return Some(n.min(6));
+    }
+    TIER_NAMES
+        .iter()
+        .position(|t| t.eq_ignore_ascii_case(v))
+        .map(|i| RANKS[i])
+}
 
 /// Load the `customprefix` overrides once, at boot.
 pub fn init(s: &Server) {
-    let mut a: [String; 6] = DEFAULT_SIGILS.map(String::from);
+    let mut cfg = PrefixCfg {
+        sigils: DEFAULT_SIGILS.map(String::from),
+        ranktoset: [None; 6],
+        ranktounset: [None; 6],
+        depriv: [true; 6],
+    };
     for line in s.conf_all("customprefix") {
         let mut it = line.split_whitespace();
-        if let (Some(name), Some(sym)) = (it.next(), it.next()) {
-            if let Some(i) = TIER_NAMES.iter().position(|t| t.eq_ignore_ascii_case(name)) {
-                if let Some(c) = sym.chars().next() {
-                    a[i] = c.to_string();
+        let Some(name) = it.next() else { continue };
+        let Some(i) = TIER_NAMES.iter().position(|t| t.eq_ignore_ascii_case(name)) else {
+            continue;
+        };
+        for tok in it {
+            match tok.split_once('=') {
+                Some(("ranktoset", v)) => cfg.ranktoset[i] = parse_rank(v),
+                Some(("ranktounset", v)) => cfg.ranktounset[i] = parse_rank(v),
+                Some(("depriv", v)) => cfg.depriv[i] = crate::config::yesish(v),
+                Some(_) => {}
+                None => {
+                    // a bare token is the sigil
+                    if let Some(c) = tok.chars().next() {
+                        cfg.sigils[i] = c.to_string();
+                    }
                 }
             }
         }
     }
-    let _ = SIGILS.set(a);
+    let _ = CFG.set(cfg);
 }
 
 /// The sigil for tier `i` (0 = oper … 5 = voice).
 pub fn sigil(i: usize) -> &'static str {
-    SIGILS
-        .get()
-        .map(|a| a[i].as_str())
+    CFG.get()
+        .map(|c| c.sigils[i].as_str())
         .unwrap_or(DEFAULT_SIGILS[i])
 }
 
-/// The prefix mode letter for a sigil char (used by the FJOIN decode); `' '` if the
-/// char isn't a prefix sigil.
+/// The prefix mode letter for a sigil char (FJOIN decode); `' '` if none.
 pub fn letter_for_sigil(c: char) -> char {
     let cs = c.to_string();
     (0..6)
@@ -57,8 +95,31 @@ pub fn letter_for_sigil(c: char) -> char {
         .unwrap_or(' ')
 }
 
-/// The ISUPPORT `PREFIX=(modes)symbols` token; `include_oper` adds the `y` tier
-/// (operprefix/ojoin).
+fn index_for_letter(letter: char) -> Option<usize> {
+    LETTERS.iter().position(|&l| l == letter)
+}
+
+/// Configured minimum rank to grant the prefix with mode letter `letter` (None ⇒
+/// use the prefix's own rank).
+pub fn rank_to_set(letter: char) -> Option<u8> {
+    let i = index_for_letter(letter)?;
+    CFG.get()?.ranktoset[i]
+}
+
+/// Configured minimum rank to revoke the prefix (None ⇒ use the prefix's own rank).
+pub fn rank_to_unset(letter: char) -> Option<u8> {
+    let i = index_for_letter(letter)?;
+    CFG.get()?.ranktounset[i]
+}
+
+/// Whether a member may remove this prefix from themselves (default yes).
+pub fn can_depriv(letter: char) -> bool {
+    index_for_letter(letter)
+        .and_then(|i| CFG.get().map(|c| c.depriv[i]))
+        .unwrap_or(true)
+}
+
+/// The ISUPPORT `PREFIX=(modes)symbols` token; `include_oper` adds the `y` tier.
 pub fn isupport(include_oper: bool) -> String {
     let start = if include_oper { 0 } else { 1 };
     let letters: String = LETTERS[start..].iter().collect();