diff --git a/SEQUENTIA.md b/SEQUENTIA.md
index 67c2ffc0c..268498589 100644
--- a/SEQUENTIA.md
+++ b/SEQUENTIA.md
@@ -448,7 +448,9 @@ The fork is not published to npm; consumers build `pkg/` with `wasm-pack`.
   are the transaction's other inputs, `[]` for a coin spent alone. `limits` is
   `{ feeFloorPerKvb }` for the specification's fee margin or
   `{ maxUncommitted }` for a ceiling in atoms; without it a rebind must commit
-  the whole coin.
+  the whole coin. A message, a source, an output or input, or `limits` with a
+  field it does not name is refused (`unknown field ...`), so a misspelt field
+  never quietly takes a default.
 - `src/ark.rs`: Arca leaves. `arkNewOwnerNonce()`, `arkLeafKeyPath(account,
   ownerNonce)`, `Signer.arkLeafKey(account, ownerNonce)` and
   `Signer.arkRestoreKey(account, record)` for the leaf keys;
@@ -459,7 +461,9 @@ The fork is not published to npm; consumers build `pkg/` with `wasm-pack`.
   chain's median time `now` as its last argument (the policy names none, and
   refuses one), whose verdict is
   `{ accepted: true, leafId, roundTxid, asset, value, expiries, ... }` or
-  `{ accepted: false, failed, check, kind, reason }`; and `ArkStore(storage)`
+  `{ accepted: false, failed, check, kind, reason }`; a policy with a field
+  it does not name is refused, as a misspelt bound would otherwise take its
+  default; and `ArkStore(storage)`
   over a `JsStorage` object, with `putPending`, `putLeaf`, `putRestoredLeaf`
   and `removeLeaf` keeping the same rules as the native store. A record is its JSON text or its binary form as
   hex. Asset ids, the token and the genesis hash are display hex at this
diff --git a/lwk_wasm/src/ark.rs b/lwk_wasm/src/ark.rs
index 06e690393..d27675e1d 100644
--- a/lwk_wasm/src/ark.rs
+++ b/lwk_wasm/src/ark.rs
@@ -37,6 +37,19 @@ fn generic(e: impl std::fmt::Display) -> Error {
     Error::Generic(e.to_string())
 }
 
+/// Read a plain object from JavaScript into `T`, refusing any field `T` does
+/// not name, at every level.
+///
+/// `serde_wasm_bindgen` reads a struct by asking the object for each field the
+/// struct names, so a field it does not name is never seen and
+/// `deny_unknown_fields` has nothing to refuse: a misspelt bound would quietly
+/// take its default. The object is read whole first, every key with it, and
+/// then into `T`, where `deny_unknown_fields` applies.
+pub(crate) fn from_js<T: serde::de::DeserializeOwned>(value: JsValue) -> Result<T, Error> {
+    let whole: serde_json::Value = serde_wasm_bindgen::from_value(value)?;
+    Ok(serde_json::from_value(whole)?)
+}
+
 fn refused(e: &RecordError) -> Error {
     Error::Generic(format!("record refused (kind {}): {e}", e.kind()))
 }
@@ -194,8 +207,8 @@ pub fn ark_parse_record(record: &str) -> Result<JsValue, Error> {
 #[serde(rename_all = "camelCase", deny_unknown_fields)]
 struct PolicyDto {
     operator: String,
-    /// Refused when present: `now` is given to each call. Named here because
-    /// an object read from JavaScript ignores fields the struct does not name.
+    /// Refused when present, with its own message: `now` is given to each
+    /// call.
     now: Option<serde::de::IgnoredAny>,
     min_notice_seconds: Option<u64>,
     horizon_seconds: Option<u32>,
@@ -207,7 +220,7 @@ struct PolicyDto {
 }
 
 #[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
+#[serde(rename_all = "camelCase", deny_unknown_fields)]
 struct FeeRateFloorDto {
     floor_per_kvb: u64,
     multiple: u64,
@@ -319,7 +332,8 @@ impl VerdictDto {
 ///
 /// The policy object is `{ operator, minNoticeSeconds?, horizonSeconds?,
 /// minExitDelaySeconds?, maxExitDelaySeconds?, maxLevels?, minReserveAtoms?,
-/// minReserveFeeRate? }`: the operator key the wallet was told (x-only hex)
+/// minReserveFeeRate? }`, refusing any field it does not name: the operator key
+/// the wallet was told (x-only hex)
 /// and the bounds, which default to the specification's (a notice of at least
 /// 36 hours, a first expiry at least 27 days after now for a leaf taken from a
 /// round, an exit delay of 36 to 48 hours, a path of at most 5 levels, and a
@@ -358,7 +372,7 @@ impl ArkVerifier {
     /// A verifier for `network` with the `policy` object described above.
     #[wasm_bindgen(constructor)]
     pub fn new(network: &Network, policy: JsValue) -> Result<ArkVerifier, Error> {
-        let dto: PolicyDto = serde_wasm_bindgen::from_value(policy)?;
+        let dto: PolicyDto = from_js(policy)?;
         if dto.now.is_some() {
             return Err(generic(
                 "the policy takes no `now`: give the chain's median time to each call",
diff --git a/lwk_wasm/src/csfs.rs b/lwk_wasm/src/csfs.rs
index bd1535abb..23eb50261 100644
--- a/lwk_wasm/src/csfs.rs
+++ b/lwk_wasm/src/csfs.rs
@@ -26,6 +26,10 @@
 //! `htlc-refund-both` and `leafId` is the id of the leaf the output is, or
 //! was made from.
 //!
+//! Every object here, the message, its source, outputs and inputs, and the
+//! `limits` of `signCsfs`, is refused when it carries a field it does not
+//! name, so a misspelt field never quietly takes a default.
+//!
 //! A rebind's `otherInputs` are the transaction's other inputs, `[]` when the
 //! coin is spent alone; for a reassignment, every other checkpoint. What the
 //! transaction leaves to whoever broadcasts is reckoned over all of them.
@@ -64,7 +68,7 @@ impl Atoms {
 }
 
 #[derive(Deserialize)]
-#[serde(rename_all = "camelCase")]
+#[serde(rename_all = "camelCase", deny_unknown_fields)]
 struct OutputDto {
     asset: String,
     value: Atoms,
@@ -72,6 +76,7 @@ struct OutputDto {
 }
 
 #[derive(Deserialize)]
+#[serde(deny_unknown_fields)]
 struct InputDto {
     asset: String,
     value: Atoms,
@@ -92,15 +97,28 @@ struct NamedSourceDto {
     salt: String,
 }
 
-#[derive(Deserialize)]
-#[serde(untagged)]
+/// A source is `{ record }` when it names a record, and the named form
+/// otherwise; each refuses fields it does not name, which an untagged enum
+/// would report only as matching no variant.
 enum SourceDto {
     Record(RecordSourceDto),
     Named(NamedSourceDto),
 }
 
+impl<'de> Deserialize<'de> for SourceDto {
+    fn deserialize<D: serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
+        let v = serde_json::Value::deserialize(d)?;
+        let source = if v.get("record").is_some() {
+            serde_json::from_value(v).map(SourceDto::Record)
+        } else {
+            serde_json::from_value(v).map(SourceDto::Named)
+        };
+        source.map_err(serde::de::Error::custom)
+    }
+}
+
 #[derive(Deserialize)]
-#[serde(tag = "kind", rename_all = "camelCase")]
+#[serde(tag = "kind", rename_all = "camelCase", deny_unknown_fields)]
 enum MessageDto {
     #[serde(rename_all = "camelCase")]
     Rebind {
@@ -180,7 +198,7 @@ pub(crate) fn parse_limits(limits: JsValue, genesis_hash: BlockHash) -> Result<C
     let dto: LimitsDto = if limits.is_undefined() || limits.is_null() {
         LimitsDto::default()
     } else {
-        serde_wasm_bindgen::from_value(limits)?
+        crate::ark::from_js(limits)?
     };
     Ok(match (dto.fee_floor_per_kvb, dto.max_uncommitted) {
         (Some(_), Some(_)) => {
@@ -196,7 +214,7 @@ pub(crate) fn parse_limits(limits: JsValue, genesis_hash: BlockHash) -> Result<C
 
 /// Parse a message object into the signer's typed message.
 pub(crate) fn parse_message(message: JsValue) -> Result<ArcaMessage, Error> {
-    let dto: MessageDto = serde_wasm_bindgen::from_value(message)?;
+    let dto: MessageDto = crate::ark::from_js(message)?;
     Ok(match dto {
         MessageDto::Rebind {
             source: src,
diff --git a/lwk_wasm/tests/node/arca_signers.js b/lwk_wasm/tests/node/arca_signers.js
index 199bd6979..94e496cc3 100644
--- a/lwk_wasm/tests/node/arca_signers.js
+++ b/lwk_wasm/tests/node/arca_signers.js
@@ -167,6 +167,16 @@ assert.throws(() => signer.signCsfs('m/6/0', rebindElsewhere, lwk.csfsDigest(reb
     /not this wallet's/);
 assert.throws(() => lwk.csfsDigest({ ...rebind, source: { ...rebind.source, path: 'exit' } }), /unknown rebindable path/);
 
+// A field a message, a source, an output or the limits do not name is refused,
+// not ignored: a misspelt ceiling would otherwise take its default.
+assert.throws(() => signer.signCsfs('m/6/0', rebind, d, { maxUncomitted: '9999000' }), /unknown field `maxUncomitted`/);
+assert.throws(() => lwk.csfsDigest({ ...rebind, source: { ...rebind.source, salts: '07'.repeat(32) } }), /unknown field `salts`/);
+assert.throws(() => lwk.csfsDigest({ ...rebind, source: { record: 'ab', leafId: 'a1'.repeat(32) } }), /unknown field `leafId`/);
+assert.throws(() => lwk.csfsDigest({ ...rebind, outputs: [{ ...rebind.outputs[0], amount: 5 }] }), /unknown field `amount`/);
+assert.throws(() => lwk.csfsDigest({ ...rebind, otherInputs: [{ asset: X, value: 1, vout: 0 }] }), /unknown field `vout`/);
+assert.throws(() => lwk.csfsDigest({ ...unroll, tme: 5 }), /unknown field `tme`/);
+assert.throws(() => lwk.csfsDigest({ ...release, connectorAsset: X }), /unknown field `connectorAsset`/);
+
 // What a reassignment leaves is reckoned over every input (review R4, F9):
 // a checkpoint of 100,000 atoms over outputs of 150,000 and 10,000.
 const spk = (b) => '5120' + b.repeat(32);
diff --git a/lwk_wasm/tests/node/ark_records.js b/lwk_wasm/tests/node/ark_records.js
index c00872b4f..8f1ed4568 100644
--- a/lwk_wasm/tests/node/ark_records.js
+++ b/lwk_wasm/tests/node/ark_records.js
@@ -86,6 +86,10 @@ const shallow = verifier({ maxLevels: 1 }).verifyLeaf(dr.json, deep.round.tx, dl
 assert.strictEqual(shallow.accepted, false);
 assert.ok(/a path of \d+ levels; the wallet accepts 1 at most/.test(shallow.reason), shallow.reason);
 assert.throws(() => verifier({ minReserveAtoms: 0, minReserveFeeRate: { floorPerKvb: 1, multiple: 1 } }), /not both/);
+// A field the policy does not name is refused, not ignored: a misspelt bound
+// would otherwise take its default without a word.
+assert.throws(() => verifier({ maxExitDelaySecond: 172800 }), /unknown field `maxExitDelaySecond`/);
+assert.throws(() => verifier({ minReserveFeeRate: { floorPerKvb: 1, multiple: 1, mutliple: 4 } }), /unknown field `mutliple`/);
 
 // 2. The refusal vectors, by kind, from both the reader and the verifier.
 const any = v.batches[1];