diff --git a/changelog.d/2-features/mls-x509-improvements b/changelog.d/2-features/mls-x509-improvements
new file mode 100644
index 0000000000..36e3d457df
--- /dev/null
+++ b/changelog.d/2-features/mls-x509-improvements
@@ -0,0 +1 @@
+The public key in an x509 credential is now checked against that of the client
diff --git a/libs/wire-api/src/Wire/API/MLS/KeyPackage.hs b/libs/wire-api/src/Wire/API/MLS/KeyPackage.hs
index 568943c026..c3bc1855b6 100644
--- a/libs/wire-api/src/Wire/API/MLS/KeyPackage.hs
+++ b/libs/wire-api/src/Wire/API/MLS/KeyPackage.hs
@@ -23,7 +23,7 @@ module Wire.API.MLS.KeyPackage
     KeyPackageData (..),
     DeleteKeyPackages (..),
     KeyPackage (..),
-    credentialIdentity,
+    credentialIdentityAndKey,
     keyPackageIdentity,
     kpRef,
     kpRef',
@@ -231,9 +231,9 @@ instance HasField "extensions" KeyPackage [Extension] where
 instance HasField "leafNode" KeyPackage LeafNode where
   getField = (.tbs.value.leafNode)
 
-credentialIdentity :: Credential -> Either Text ClientIdentity
-credentialIdentity (BasicCredential i) = decodeMLS' i
-credentialIdentity (X509Credential certs) = do
+credentialIdentityAndKey :: Credential -> Either Text (ClientIdentity, Maybe X509.PubKey)
+credentialIdentityAndKey (BasicCredential i) = (,) <$> decodeMLS' i <*> pure Nothing
+credentialIdentityAndKey (X509Credential certs) = do
   bs <- case certs of
     [] -> Left "Invalid x509 certificate chain"
     (c : _) -> pure c
@@ -242,20 +242,20 @@ credentialIdentity (X509Credential certs) = do
       X509.decodeSignedCertificate bs
   -- FUTUREWORK: verify signature
   let cert = X509.getCertificate signed
-  certificateIdentity cert
+  certificateIdentityAndKey cert
 
 keyPackageIdentity :: KeyPackage -> Either Text ClientIdentity
-keyPackageIdentity kp = credentialIdentity kp.leafNode.credential
+keyPackageIdentity kp = fst <$> credentialIdentityAndKey kp.leafNode.credential
 
-certificateIdentity :: X509.Certificate -> Either Text ClientIdentity
-certificateIdentity cert =
+certificateIdentityAndKey :: X509.Certificate -> Either Text (ClientIdentity, Maybe X509.PubKey)
+certificateIdentityAndKey cert =
   let getNames (X509.ExtSubjectAltName names) = names
       getURI (X509.AltNameURI u) = Just u
       getURI _ = Nothing
       altNames = maybe [] getNames (X509.extensionGet (X509.certExtensions cert))
       ids = map sanIdentity (mapMaybe getURI altNames)
    in case partitionEithers ids of
-        (_, (cid : _)) -> pure cid
+        (_, (cid : _)) -> pure (cid, Just (X509.certPubKey cert))
         ((e : _), []) -> Left e
         _ -> Left "No SAN URIs found"
 
diff --git a/libs/wire-api/src/Wire/API/MLS/Validation.hs b/libs/wire-api/src/Wire/API/MLS/Validation.hs
index f97e7fc021..2f98d96942 100644
--- a/libs/wire-api/src/Wire/API/MLS/Validation.hs
+++ b/libs/wire-api/src/Wire/API/MLS/Validation.hs
@@ -23,9 +23,12 @@ module Wire.API.MLS.Validation
 where
 
 import Control.Applicative
+import Control.Error.Util
+import Data.ByteArray qualified as BA
 import Data.Text.Lazy qualified as LT
 import Data.Text.Lazy.Builder qualified as LT
 import Data.Text.Lazy.Builder.Int qualified as LT
+import Data.X509 qualified as X509
 import Imports hiding (cs)
 import Wire.API.MLS.Capabilities
 import Wire.API.MLS.CipherSuite
@@ -97,16 +100,17 @@ validateLeafNode cs mIdentity extra leafNode = do
     )
     $ Left "Invalid LeafNode signature"
 
-  validateCredential mIdentity leafNode.credential
+  validateCredential cs leafNode.signatureKey mIdentity leafNode.credential
   validateSource extra.tag leafNode.source
   validateCapabilities (credentialTag leafNode.credential) leafNode.capabilities
 
-validateCredential :: Maybe ClientIdentity -> Credential -> Either Text ()
-validateCredential mIdentity cred = do
+validateCredential :: CipherSuiteTag -> ByteString -> Maybe ClientIdentity -> Credential -> Either Text ()
+validateCredential cs pkey mIdentity cred = do
   -- FUTUREWORK: check signature in the case of an x509 credential
-  identity <-
+  (identity, mkey) <-
     either credentialError pure $
-      credentialIdentity cred
+      credentialIdentityAndKey cred
+  traverse_ (validateCredentialKey (csSignatureScheme cs) pkey) mkey
   unless (maybe True (identity ==) mIdentity) $
     Left "client identity does not match credential identity"
   where
@@ -114,6 +118,11 @@ validateCredential mIdentity cred = do
       Left $
         "Failed to parse identity: " <> e
 
+validateCredentialKey :: SignatureSchemeTag -> ByteString -> X509.PubKey -> Either Text ()
+validateCredentialKey Ed25519 pk1 (X509.PubKeyEd25519 pk2) =
+  note "Certificate public key does not match client's" $ guard (pk1 == BA.convert pk2)
+validateCredentialKey _ _ _ = Left "Certificate signature scheme does not match client's public key"
+
 validateSource :: LeafNodeSourceTag -> LeafNodeSource -> Either Text ()
 validateSource t s = do
   let t' = leafNodeSourceTag s
diff --git a/nix/pkgs/mls-test-cli/default.nix b/nix/pkgs/mls-test-cli/default.nix
index bbaab19f30..7cd0852fd4 100644
--- a/nix/pkgs/mls-test-cli/default.nix
+++ b/nix/pkgs/mls-test-cli/default.nix
@@ -13,8 +13,8 @@ let
   src = fetchFromGitHub {
     owner = "wireapp";
     repo = "mls-test-cli";
-    rev = "d16b4e9d4e93b731e81cd04a00620f2c6a36e696";
-    sha256 = "sha256-2p5m6R80dnyJShAvjmO+ZbX8wxMtuFmvPnp9uX4eezc=";
+    rev = "e6e6ce0c29f0e48e84b4ccef058130aca0625492";
+    sha256 = "sha256-J9M8w3GJnULH3spKEuPGCL/t43zb2Wd+YfZ0LY3YITo=";
   };
   cargoLockFile = builtins.toFile "cargo.lock" (builtins.readFile "${src}/Cargo.lock");
 in rustPlatform.buildRustPackage rec {