diff --git a/packages/snap/CHANGELOG.md b/packages/snap/CHANGELOG.md
index 3025bde4..f912f95b 100644
--- a/packages/snap/CHANGELOG.md
+++ b/packages/snap/CHANGELOG.md
@@ -11,6 +11,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Validate that account IDs passed to `keyring_setSelectedAccounts` belong to the snap, rejecting unknown IDs with `InvalidParamsError` ([#604](https://github.com/MetaMask/snap-solana-wallet/pull/604))
 
+### Fixed
+
+- **BREAKING:** `signTransaction` and `signAllTransactions` now preserve the original `messageBytes` of a compiled `VersionedTransaction` verbatim and only append the account's signature (#[0000](https://github.com/MetaMask/snap-solana-wallet/pull/0000))
+  - Previously, an unsigned compiled transaction was silently decompiled and recompiled, which canonicalised the account order and remapped instruction account indices — breaking multi-party signing flows.
+
 ## [2.8.0]
 
 ### Added
diff --git a/packages/snap/snap.manifest.json b/packages/snap/snap.manifest.json
index 26c0286f..d910258e 100644
--- a/packages/snap/snap.manifest.json
+++ b/packages/snap/snap.manifest.json
@@ -7,7 +7,7 @@
     "url": "https://github.com/MetaMask/snap-solana-wallet.git"
   },
   "source": {
-    "shasum": "AzXzPnYm37l2ijVy4ZM6GRu3DouI8hs75QHbfXJ/sBQ=",
+    "shasum": "2hll3bYQPDYuEYTjkPO0FSfFD9j7c/++LaL9SHU1BrI=",
     "location": {
       "npm": {
         "filePath": "dist/bundle.js",
diff --git a/packages/snap/src/core/services/signer/Signer.ts b/packages/snap/src/core/services/signer/Signer.ts
index 51211f2e..e2bc8623 100644
--- a/packages/snap/src/core/services/signer/Signer.ts
+++ b/packages/snap/src/core/services/signer/Signer.ts
@@ -95,29 +95,14 @@ export class Signer {
       );
     }
 
-    const isUnsigned = Object.values(
-      transactionMessageOrTransaction.signatures,
-    ).every((signature) => !signature);
-
-    // It's an unsigned transaction, grab the message from the transaction and apply the same logic as above.
-    if (isUnsigned) {
-      const { messageBytes } = transactionMessageOrTransaction;
-
-      const transactionMessageFromUnsignedTransaction =
-        await fromBytesToCompilableTransactionMessage(
-          messageBytes,
-          rpc,
-          config,
-        );
-
-      return this.#prepareAndPartiallySignTransactionMessage(
-        transactionMessageFromUnsignedTransaction,
-        account,
-        network,
-      );
-    }
-
-    // It's a partially signed transaction, so we cannot alter its content, and we add the account's signature.
+    // It's a compiled transaction (either unsigned or partially signed).
+    // Per the Wallet Standard `signTransaction` contract, we MUST NOT mutate
+    // the message bytes — only append the account's signature. Decompiling and
+    // recompiling here would canonicalise the account ordering and remap
+    // instruction account indices, breaking multi-party signing flows where
+    // a counterparty has already signed the original bytes
+    //
+    // See: https://consensyssoftware.atlassian.net/browse/WPN-1035
     return this.#partiallySignTransaction(
       transactionMessageOrTransaction,
       account,