diff --git a/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/helpers.nr b/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/helpers.nr
index b7ebba92e7d7..71e4341f8afa 100644
--- a/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/helpers.nr
+++ b/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/helpers.nr
@@ -91,8 +91,20 @@ pub(crate) comptime fn create_authorize_once_check(f: FunctionDefinition, is_pri
     let nonce_check_quote = f"{nonce_arg_name_quoted} == 0".quoted_contents();
 
     let fn_call = if is_private {
-        let args_len = f.parameters().len();
-        quote { aztec::authwit::auth::assert_current_call_valid_authwit::<$args_len> }
+        let params = f.parameters();
+        let serialized_len_quote = if params.len() == 0 {
+            quote { 0 }
+        } else {
+            let params_quote_without_parentheses = params
+                .map(|(_, param_type): (Quoted, Type)| {
+                    quote {
+                    <$param_type as aztec::protocol::traits::Serialize>::N
+                }
+                })
+                .join(quote {+});
+            quote { ($params_quote_without_parentheses) }
+        };
+        quote { aztec::authwit::auth::assert_current_call_valid_authwit::<($serialized_len_quote)> }
     } else {
         quote { aztec::authwit::auth::assert_current_call_valid_authwit_public }
     };
diff --git a/noir-projects/noir-contracts/contracts/test/auth_wit_test_contract/src/main.nr b/noir-projects/noir-contracts/contracts/test/auth_wit_test_contract/src/main.nr
index aad212668b38..6f78d6b58c3a 100644
--- a/noir-projects/noir-contracts/contracts/test/auth_wit_test_contract/src/main.nr
+++ b/noir-projects/noir-contracts/contracts/test/auth_wit_test_contract/src/main.nr
@@ -4,10 +4,17 @@ use aztec::macros::aztec;
 pub contract AuthWitTest {
     use aztec::{
         authwit::auth::{assert_inner_hash_valid_authwit, assert_inner_hash_valid_authwit_public},
-        macros::functions::external,
-        protocol::address::AztecAddress,
+        macros::functions::{authorize_once, external},
+        protocol::{address::AztecAddress, traits::{Deserialize, Serialize}},
     };
 
+    #[derive(Serialize, Deserialize)]
+    pub struct MultiFieldStruct {
+        pub a: Field,
+        pub b: Field,
+        pub c: Field,
+    }
+
     #[external("private")]
     fn consume(on_behalf_of: AztecAddress, inner_hash: Field) {
         assert_inner_hash_valid_authwit(self.context, on_behalf_of, inner_hash);
@@ -17,4 +24,16 @@ pub contract AuthWitTest {
     fn consume_public(on_behalf_of: AztecAddress, inner_hash: Field) {
         assert_inner_hash_valid_authwit_public(self.context, on_behalf_of, inner_hash);
     }
+
+    /// Regression test for #[authorize_once] with a struct parameter that serializes to 3 fields.
+    /// The macro must emit assert_current_call_valid_authwit::<6>
+    /// (from:1 + data:3 + amount:1 + nonce:1), not ::<4> (parameter count).
+    #[authorize_once("from", "authwit_nonce")]
+    #[external("private")]
+    fn auth_with_struct(
+        from: AztecAddress,
+        _data: MultiFieldStruct,
+        _amount: Field,
+        authwit_nonce: Field,
+    ) {}
 }
diff --git a/yarn-project/end-to-end/src/e2e_kernelless_simulation.test.ts b/yarn-project/end-to-end/src/e2e_kernelless_simulation.test.ts
index 13d359ff5b46..ee283d050d64 100644
--- a/yarn-project/end-to-end/src/e2e_kernelless_simulation.test.ts
+++ b/yarn-project/end-to-end/src/e2e_kernelless_simulation.test.ts
@@ -5,12 +5,15 @@ import type { Logger } from '@aztec/aztec.js/log';
 import type { AztecNode } from '@aztec/aztec.js/node';
 import { AMMContract } from '@aztec/noir-contracts.js/AMM';
 import { type TokenContract, TokenContractArtifact } from '@aztec/noir-contracts.js/Token';
+import { AuthWitTestContract, AuthWitTestContractArtifact } from '@aztec/noir-test-contracts.js/AuthWitTest';
+import { GenericProxyContract } from '@aztec/noir-test-contracts.js/GenericProxy';
 import { PendingNoteHashesContract } from '@aztec/noir-test-contracts.js/PendingNoteHashes';
 import { type AbiDecoded, decodeFromAbi, getFunctionArtifact } from '@aztec/stdlib/abi';
 import { computeOuterAuthWitHash } from '@aztec/stdlib/auth-witness';
 
 import { jest } from '@jest/globals';
 
+import { simulateThroughAuthwitProxy } from './fixtures/authwit_proxy.js';
 import { deployToken, mintTokensToPrivate } from './fixtures/token_utils.js';
 import { setup } from './fixtures/utils.js';
 import type { TestWallet } from './test-wallet/test_wallet.js';
@@ -328,6 +331,63 @@ describe('Kernelless simulation', () => {
     });
   });
 
+  describe('authorize_once with multi-field struct parameters', () => {
+    let authWitTestContract: AuthWitTestContract;
+    let proxy: GenericProxyContract;
+
+    beforeAll(async () => {
+      [{ contract: authWitTestContract }, { contract: proxy }] = await Promise.all([
+        AuthWitTestContract.deploy(wallet).send({ from: adminAddress }),
+        GenericProxyContract.deploy(wallet).send({ from: adminAddress }),
+      ]);
+    });
+
+    it('emits offchain effect with correct serialized args length for struct parameters', async () => {
+      const structData = { a: Fr.random(), b: Fr.random(), c: Fr.random() };
+      const amount = Fr.random();
+      const nonce = Fr.random();
+
+      // This function uses a struct with 3 fields as parameter, and the #[authorize_once] macro should correctly
+      // account for this and emit a CallAuthorizationRequest with the correct serialized length, rather than
+      // just the arguments length
+      const interaction = authWitTestContract.methods.auth_with_struct(adminAddress, structData, amount, nonce);
+
+      wallet.setSimulationMode('kernelless-override');
+      const { offchainEffects } = await simulateThroughAuthwitProxy(proxy, interaction, {
+        from: adminAddress,
+        includeMetadata: true,
+      });
+
+      expect(offchainEffects.length).toBe(1);
+
+      const callAuthRequest = await CallAuthorizationRequest.fromFields(offchainEffects[0].data);
+
+      expect(offchainEffects[0].contractAddress).toEqual(authWitTestContract.address);
+
+      // The macro should emit 6 arguments in total before decoding: from (1) + struct (3) + amount (1) + nonce (1)
+      expect(callAuthRequest.args).toHaveLength(6);
+
+      expect(callAuthRequest.onBehalfOf).toEqual(adminAddress);
+      expect(callAuthRequest.msgSender).toEqual(proxy.address);
+
+      const functionAbi = await getFunctionArtifact(AuthWitTestContractArtifact, callAuthRequest.functionSelector);
+      const decodedArgs = decodeFromAbi(
+        functionAbi.parameters.map(param => param.type),
+        callAuthRequest.args,
+      ) as AbiDecoded[];
+
+      expect(decodedArgs).toHaveLength(4);
+      expect(decodedArgs[0]).toEqual(adminAddress);
+      expect(decodedArgs[1]).toEqual({
+        a: structData.a.toBigInt(),
+        b: structData.b.toBigInt(),
+        c: structData.c.toBigInt(),
+      });
+      expect(decodedArgs[2]).toEqual(amount.toBigInt());
+      expect(decodedArgs[3]).toEqual(nonce.toBigInt());
+    });
+  });
+
   describe('read request verification', () => {
     let pendingNoteHashesContract: PendingNoteHashesContract;
 
diff --git a/yarn-project/end-to-end/src/fixtures/authwit_proxy.ts b/yarn-project/end-to-end/src/fixtures/authwit_proxy.ts
index 044d7f9ae34e..a98ecaf26082 100644
--- a/yarn-project/end-to-end/src/fixtures/authwit_proxy.ts
+++ b/yarn-project/end-to-end/src/fixtures/authwit_proxy.ts
@@ -17,6 +17,10 @@ async function buildProxyCall(proxy: GenericProxyContract, action: ContractFunct
     return proxy.methods.forward_private_3(call.to, call.selector, call.args);
   } else if (argCount === 4) {
     return proxy.methods.forward_private_4(call.to, call.selector, call.args);
+  } else if (argCount === 5) {
+    return proxy.methods.forward_private_5(call.to, call.selector, call.args);
+  } else if (argCount === 6) {
+    return proxy.methods.forward_private_6(call.to, call.selector, call.args);
   }
   throw new Error(`No forward_private_${argCount} method on proxy`);
 }