diff --git a/CHANGELOG.md b/CHANGELOG.md
index cfd2f7c..4615c50 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Add `AuthenticatorConfig` command.
   - Add `credBlob` extension and split `make_credential::Extensions` into `ExtensionsInput` and `ExtensionsOutput`.
   - Add `minPinLength` extension.
+- Add support for missing CTAP 2.2 features:
+  - Add `hmac-secret-mc` extension.
 
 ## [0.5.0] 2026-03-23
 
diff --git a/src/arbitrary.rs b/src/arbitrary.rs
index 4bf3180..ae04757 100644
--- a/src/arbitrary.rs
+++ b/src/arbitrary.rs
@@ -308,6 +308,7 @@ impl<'a> Arbitrary<'a> for ctap2::make_credential::ExtensionsInput<'a> {
         } else {
             None
         };
+        let hmac_secret_mc = u.arbitrary()?;
         Ok(Self {
             cred_protect,
             hmac_secret,
@@ -315,6 +316,7 @@ impl<'a> Arbitrary<'a> for ctap2::make_credential::ExtensionsInput<'a> {
             #[cfg(feature = "third-party-payment")]
             third_party_payment,
             cred_blob,
+            hmac_secret_mc,
         })
     }
 }
diff --git a/src/ctap2/get_info.rs b/src/ctap2/get_info.rs
index 2736791..00d6814 100644
--- a/src/ctap2/get_info.rs
+++ b/src/ctap2/get_info.rs
@@ -14,7 +14,7 @@ pub struct Response {
 
     // 0x02
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub extensions: Option<Vec<Extension, 6>>,
+    pub extensions: Option<Vec<Extension, 7>>,
 
     // 0x03
     pub aaguid: Bytes<16>,
@@ -252,6 +252,7 @@ pub enum Extension {
     CredProtect,
     CredBlob,
     HmacSecret,
+    HmacSecretMc,
     LargeBlobKey,
     MinPinLength,
     ThirdPartyPayment,
@@ -261,6 +262,7 @@ impl Extension {
     const CRED_PROTECT: &'static str = "credProtect";
     const CRED_BLOB: &'static str = "credBlob";
     const HMAC_SECRET: &'static str = "hmac-secret";
+    const HMAC_SECRET_MC: &'static str = "hmac-secret-mc";
     const LARGE_BLOB_KEY: &'static str = "largeBlobKey";
     const MIN_PIN_LENGTH: &'static str = "minPinLength";
     const THIRD_PARTY_PAYMENT: &'static str = "thirdPartyPayment";
@@ -272,6 +274,7 @@ impl From<Extension> for &str {
             Extension::CredProtect => Extension::CRED_PROTECT,
             Extension::CredBlob => Extension::CRED_BLOB,
             Extension::HmacSecret => Extension::HMAC_SECRET,
+            Extension::HmacSecretMc => Extension::HMAC_SECRET_MC,
             Extension::LargeBlobKey => Extension::LARGE_BLOB_KEY,
             Extension::MinPinLength => Extension::MIN_PIN_LENGTH,
             Extension::ThirdPartyPayment => Extension::THIRD_PARTY_PAYMENT,
@@ -287,6 +290,7 @@ impl TryFrom<&str> for Extension {
             Self::CRED_PROTECT => Ok(Self::CredProtect),
             Self::CRED_BLOB => Ok(Self::CredBlob),
             Self::HMAC_SECRET => Ok(Self::HmacSecret),
+            Self::HMAC_SECRET_MC => Ok(Self::HmacSecretMc),
             Self::LARGE_BLOB_KEY => Ok(Self::LargeBlobKey),
             Self::MIN_PIN_LENGTH => Ok(Self::MinPinLength),
             Self::THIRD_PARTY_PAYMENT => Ok(Self::ThirdPartyPayment),
@@ -475,6 +479,7 @@ mod tests {
             (Extension::CredProtect, "credProtect"),
             (Extension::CredBlob, "credBlob"),
             (Extension::HmacSecret, "hmac-secret"),
+            (Extension::HmacSecretMc, "hmac-secret-mc"),
             (Extension::LargeBlobKey, "largeBlobKey"),
             (Extension::MinPinLength, "minPinLength"),
             (Extension::ThirdPartyPayment, "thirdPartyPayment"),
diff --git a/src/ctap2/make_credential.rs b/src/ctap2/make_credential.rs
index 534a13a..daeabc2 100644
--- a/src/ctap2/make_credential.rs
+++ b/src/ctap2/make_credential.rs
@@ -51,6 +51,13 @@ pub struct ExtensionsInput<'a> {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub large_blob_key: Option<bool>,
 
+    /// `hmac-secret-mc` (CTAP 2.2 §11.4.5 / WebAuthn L3): platform-supplied
+    /// hmac-secret request evaluated at MakeCredential time, returning
+    /// hmac-secret outputs alongside the freshly-minted credential.
+    #[serde(rename = "hmac-secret-mc")]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub hmac_secret_mc: Option<super::get_assertion::HmacSecretInput>,
+
     #[cfg(feature = "third-party-payment")]
     #[serde(rename = "thirdPartyPayment")]
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -77,6 +84,13 @@ pub struct ExtensionsOutput {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub hmac_secret: Option<bool>,
 
+    /// `hmac-secret-mc` (CTAP 2.2): encrypted hmac-secret outputs produced at
+    /// MakeCredential time. Wire format mirrors GetAssertion's `hmac-secret`
+    /// output — `enc(output1)` or `enc(output1 || output2)`, up to 80 bytes.
+    #[serde(rename = "hmac-secret-mc")]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub hmac_secret_mc: Option<crate::Bytes<80>>,
+
     #[cfg(feature = "third-party-payment")]
     #[serde(rename = "thirdPartyPayment")]
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -190,6 +204,8 @@ pub struct UnsignedExtensionOutputs {}
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::ctap2::get_assertion::HmacSecretInput;
+    use cosey::EcdhEsHkdf256PublicKey;
     use serde_test::{assert_ser_tokens, Token};
 
     #[test]
@@ -223,6 +239,15 @@ mod tests {
             #[cfg(feature = "third-party-payment")]
             third_party_payment: Some(true),
             cred_blob: Some(serde_bytes::Bytes::new(b"1234")),
+            hmac_secret_mc: Some(HmacSecretInput {
+                key_agreement: EcdhEsHkdf256PublicKey {
+                    x: [0xff; 32].try_into().unwrap(),
+                    y: [0xff; 32].try_into().unwrap(),
+                },
+                salt_enc: [0xff; 80].try_into().unwrap(),
+                salt_auth: [0xff; 32].try_into().unwrap(),
+                pin_protocol: Some(1),
+            }),
         };
         crate::test::assert_canonical_cbor(&extensions);
     }
@@ -235,6 +260,7 @@ mod tests {
             #[cfg(feature = "third-party-payment")]
             third_party_payment: Some(true),
             cred_blob: Some(true),
+            hmac_secret_mc: Some([0xff; 80].try_into().unwrap()),
         };
         crate::test::assert_canonical_cbor(&extensions);
     }