diff --git a/Cargo.lock b/Cargo.lock
index 53fc6a7..67ba8a4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2631,6 +2631,7 @@ dependencies = [
  "rusqlite",
  "safelog",
  "serde_json",
+ "sha3 0.10.9",
  "snow",
  "tempfile",
  "tokio",
diff --git a/Cargo.toml b/Cargo.toml
index 9131d4b..342d15c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -43,6 +43,7 @@ snow = "0.10"
 serde_json = "1"
 argon2 = "0.5"
 chacha20poly1305 = "0.10"
+sha3 = "0.10"
 
 [dev-dependencies]
 tempfile = "3"
diff --git a/src/pay.rs b/src/pay.rs
index faae2dd..2f79d43 100644
--- a/src/pay.rs
+++ b/src/pay.rs
@@ -1,4 +1,5 @@
 use ed25519_dalek::{Signature, Signer, SigningKey, Verifier, VerifyingKey};
+use sha3::{Digest, Keccak256};
 
 pub type Result<T> = std::result::Result<T, Error>;
 
@@ -35,19 +36,72 @@ const INV_PREFIX: &[u8] = b"inv ";
 const RCP_PREFIX: &[u8] = b"rcp ";
 const PICONERO: u128 = 1_000_000_000_000;
 
+/// Bitcoin-style alphabet; Monero encodes 8-byte blocks (11 chars), not raw base58.
+const B58: &[u8] = b"123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
+const B58_ENC_LEN: [usize; 9] = [0, 2, 3, 5, 6, 7, 9, 10, 11];
+
 pub fn check_address(addr: &str) -> Result<()> {
-    let ok = match addr.as_bytes().first() {
-        Some(b'4') if addr.len() == 95 || addr.len() == 106 => true,
-        Some(b'8') if addr.len() == 95 => true,
+    let raw = decode_monero_b58(addr).ok_or_else(|| Error("invalid Monero address".into()))?;
+    if raw.len() != 69 && raw.len() != 77 {
+        return Err(Error("invalid Monero address".into()));
+    }
+    let (payload, ck) = raw.split_at(raw.len() - 4);
+    let hash = Keccak256::digest(payload);
+    if hash.as_slice().get(..4) != Some(ck) {
+        return Err(Error("invalid Monero address".into()));
+    }
+    let ok = match (payload[0], raw.len()) {
+        (18 | 24 | 42 | 36, 69) => true, // mainnet/stagenet standard + subaddress
+        (19 | 25, 77) => true,           // mainnet/stagenet integrated
         _ => false,
     };
-    if ok && !addr.contains('\n') {
+    if ok {
         Ok(())
     } else {
         Err(Error("invalid Monero address".into()))
     }
 }
 
+fn decode_monero_b58(addr: &str) -> Option<Vec<u8>> {
+    let bytes = addr.as_bytes();
+    if bytes.is_empty() || !bytes.iter().all(|b| B58.contains(b)) {
+        return None;
+    }
+    let mut out = Vec::new();
+    let mut i = 0;
+    while i < bytes.len() {
+        let rest = bytes.len() - i;
+        let (enc_len, dec_len) = if rest >= 11 {
+            (11, 8)
+        } else {
+            let dec_len = B58_ENC_LEN.iter().position(|&n| n == rest)?;
+            (rest, dec_len)
+        };
+        out.extend_from_slice(&decode_b58_block(&bytes[i..i + enc_len], dec_len)?);
+        i += enc_len;
+    }
+    Some(out)
+}
+
+fn decode_b58_block(enc: &[u8], out_len: usize) -> Option<Vec<u8>> {
+    let mut acc: u128 = 0;
+    for &c in enc {
+        let d = B58.iter().position(|&a| a == c)? as u128;
+        acc = acc.checked_mul(58)?.checked_add(d)?;
+    }
+    let max = if out_len >= 16 {
+        return None;
+    } else if out_len == 0 {
+        0
+    } else {
+        (1u128 << (8 * out_len)) - 1
+    };
+    if acc > max {
+        return None;
+    }
+    Some(acc.to_be_bytes()[16 - out_len..].to_vec())
+}
+
 pub fn parse_atomic(s: &str) -> Result<u128> {
     if s.is_empty() || !s.bytes().all(|b| b.is_ascii_digit()) {
         return Err(Error("amount must be decimal piconero".into()));
diff --git a/src/profile.rs b/src/profile.rs
index 38228cc..81fc7d5 100644
--- a/src/profile.rs
+++ b/src/profile.rs
@@ -125,6 +125,9 @@ fn check_fields(display_name: &str, bio: &str, xmr_addr: &str) -> Result<()> {
     if display_name.contains('\n') || bio.contains('\n') || xmr_addr.contains('\n') {
         return Err(Error("profile fields must not contain newlines".into()));
     }
+    if !xmr_addr.is_empty() {
+        crate::pay::check_address(xmr_addr).map_err(|e| Error(e.to_string()))?;
+    }
     Ok(())
 }
 
diff --git a/tests/pay.rs b/tests/pay.rs
index 1cc7ffa..693e67b 100644
--- a/tests/pay.rs
+++ b/tests/pay.rs
@@ -12,16 +12,20 @@ fn store() -> (tempfile::TempDir, Store) {
     (dir, store)
 }
 
+// Official mainnet standard from Monero docs (not live RPC).
+const MAINNET_STD: &str = "4AdUndXHHZ6cfufTMvppY6JwXNouMBzSkbLYfpAV5Usx3skxNgYeYTRj5UzqtReoS44qo9mtmXCqY45DJ852K5Jv2684Rge";
+// Same documented spend/view keys, mainnet subaddress (0x2A) and integrated (0x13 + 8 zero pid).
+const MAINNET_SUB: &str = "8BTd81B7syWcfufTMvppY6JwXNouMBzSkbLYfpAV5Usx3skxNgYeYTRj5UzqtReoS44qo9mtmXCqY45DJ852K5Jv25pnJx6";
+const MAINNET_INT: &str = "4LL9oSLmtpccfufTMvppY6JwXNouMBzSkbLYfpAV5Usx3skxNgYeYTRj5UzqtReoS44qo9mtmXCqY45DJ852K5Jv2WK48GNSUQf17NLRTG";
+// Same keys, stagenet standard (0x18).
+const STAGENET_STD: &str = "5AqWsUSEwACcfufTMvppY6JwXNouMBzSkbLYfpAV5Usx3skxNgYeYTRj5UzqtReoS44qo9mtmXCqY45DJ852K5Jv23X7tqA";
+
 fn addr_std() -> String {
-    format!("4{}", "A".repeat(94))
+    MAINNET_STD.to_string()
 }
 
 fn addr_sub() -> String {
-    format!("8{}", "B".repeat(94))
-}
-
-fn addr_integrated() -> String {
-    format!("4{}", "C".repeat(105))
+    MAINNET_SUB.to_string()
 }
 
 fn payw<'a>(
@@ -46,12 +50,20 @@ fn payw<'a>(
 
 #[test]
 fn valid_and_invalid_xmr_addresses() {
-    assert!(pay::check_address(&addr_std()).is_ok());
-    assert!(pay::check_address(&addr_sub()).is_ok());
-    assert!(pay::check_address(&addr_integrated()).is_ok());
+    assert!(pay::check_address(MAINNET_STD).is_ok());
+    assert!(pay::check_address(MAINNET_SUB).is_ok());
+    assert!(pay::check_address(MAINNET_INT).is_ok());
+    assert!(pay::check_address(STAGENET_STD).is_ok());
+    // prefix+length junk that the old checker accepted
+    assert!(pay::check_address(&format!("4{}", "A".repeat(94))).is_err());
+    assert!(pay::check_address(&format!("8{}", "B".repeat(94))).is_err());
+    assert!(pay::check_address(&format!("4{}", "C".repeat(105))).is_err());
     assert!(pay::check_address(&format!("4{}", "A".repeat(93))).is_err());
     assert!(pay::check_address(&format!("8{}", "B".repeat(95))).is_err());
-    assert!(pay::check_address(&format!("5{}", "A".repeat(94))).is_err());
+    assert!(pay::check_address(&format!("{MAINNET_STD}\n")).is_err());
+    let mut bad_ck = MAINNET_STD.to_string();
+    bad_ck.replace_range(94..95, "f");
+    assert!(pay::check_address(&bad_ck).is_err());
     assert!(pay::check_address("").is_err());
     assert!(pay::check_address("not-an-address").is_err());
 }
diff --git a/tests/profile.rs b/tests/profile.rs
index e73c4a3..83453ae 100644
--- a/tests/profile.rs
+++ b/tests/profile.rs
@@ -108,21 +108,33 @@ fn chat_is_not_profile() {
     assert!(profile::decode(b"hello wire").is_none());
 }
 
+const MAINNET_STD: &str = "4AdUndXHHZ6cfufTMvppY6JwXNouMBzSkbLYfpAV5Usx3skxNgYeYTRj5UzqtReoS44qo9mtmXCqY45DJ852K5Jv2684Rge";
+
 #[test]
 fn self_profile_roundtrip() {
     let (_dir, store) = store();
-    store.set_self_profile("me", "a bio", "4abc").unwrap();
+    store.set_self_profile("me", "a bio", MAINNET_STD).unwrap();
     let got = store.self_profile().unwrap();
     assert_eq!(got.display_name, "me");
     assert_eq!(got.bio, "a bio");
-    assert_eq!(got.xmr_addr, "4abc");
+    assert_eq!(got.xmr_addr, MAINNET_STD);
     assert!(got.updated_at > 0);
     store.set_self_profile("", "", "").unwrap();
     let empty = store.self_profile().unwrap();
     assert_eq!(empty.display_name, "");
+    assert_eq!(empty.xmr_addr, "");
     assert!(empty.updated_at >= got.updated_at);
 }
 
+#[test]
+fn self_profile_rejects_short_xmr_addr() {
+    let (_dir, store) = store();
+    assert!(store.set_self_profile("me", "a bio", "4abc").is_err());
+    assert!(profile::validate("me", "a bio", "4abc").is_err());
+    assert!(profile::validate("me", "a bio", "").is_ok());
+    assert!(profile::validate("me", "a bio", MAINNET_STD).is_ok());
+}
+
 #[test]
 fn slash_profile_who_and_wipe_still_parse() {
     assert_eq!(parse_cmd("/profile"), Some(SlashCmd::Profile));