diff --git a/test/evm/hardhat/MerkleLib.Proofs.ts b/test/evm/hardhat/MerkleLib.Proofs.ts
index a0a1be168..4d3c4493d 100644
--- a/test/evm/hardhat/MerkleLib.Proofs.ts
+++ b/test/evm/hardhat/MerkleLib.Proofs.ts
@@ -12,8 +12,11 @@ import {
   BigNumber,
   ethers,
   randomBytes32,
+  bytes32ToAddress,
+  addressToBytes,
 } from "../../../utils/utils";
 import { V3RelayData, V3SlowFill } from "../../../test-utils";
+import { ParamType } from "ethers/lib/utils";
 
 let merkleLibTest: Contract;
 
@@ -149,4 +152,63 @@ describe("MerkleLib Proofs", async function () {
     expect(() => merkleTree.getHexProof(invalidLeaf)).to.throw();
     expect(await merkleLibTest.verifyV3SlowRelayFulfillment(root, invalidLeaf, proof)).to.equal(false);
   });
+  // @todo we can remove this after the new spoke pool is upgraded
+  it("Legacy V3SlowFill produces the same MerkleLeaf", async function () {
+    const chainId = randomBigNumber(2).toNumber();
+    const relayData: V3RelayData = {
+      depositor: addressToBytes(randomAddress()),
+      recipient: addressToBytes(randomAddress()),
+      exclusiveRelayer: addressToBytes(randomAddress()),
+      inputToken: addressToBytes(randomAddress()),
+      outputToken: addressToBytes(randomAddress()),
+      inputAmount: randomBigNumber(),
+      outputAmount: randomBigNumber(),
+      originChainId: randomBigNumber(2).toNumber(),
+      depositId: randomBigNumber(2),
+      fillDeadline: randomBigNumber(2).toNumber(),
+      exclusivityDeadline: randomBigNumber(2).toNumber(),
+      message: ethers.utils.hexlify(ethers.utils.randomBytes(1024)),
+    };
+    const slowLeaf: V3SlowFill = {
+      relayData,
+      chainId,
+      updatedOutputAmount: relayData.outputAmount,
+    };
+    const legacyRelayData: V3RelayData = {
+      ...relayData,
+      depositor: bytes32ToAddress(relayData.depositor),
+      recipient: bytes32ToAddress(relayData.recipient),
+      exclusiveRelayer: bytes32ToAddress(relayData.exclusiveRelayer),
+      inputToken: bytes32ToAddress(relayData.inputToken),
+      outputToken: bytes32ToAddress(relayData.outputToken),
+    };
+    const legacySlowLeaf: V3SlowFill = {
+      relayData: legacyRelayData,
+      chainId: slowLeaf.chainId,
+      updatedOutputAmount: slowLeaf.updatedOutputAmount,
+    };
+
+    const paramType = await getParamType("MerkleLibTest", "verifyV3SlowRelayFulfillment", "slowFill");
+    const hashFn = (input: V3SlowFill) => keccak256(defaultAbiCoder.encode([paramType!], [input]));
+    const merkleTree = new MerkleTree<V3SlowFill>([slowLeaf], hashFn);
+    const root = merkleTree.getHexRoot();
+
+    const legacyHashFn = (input: V3SlowFill) =>
+      keccak256(
+        defaultAbiCoder.encode(
+          [
+            "tuple(" +
+              "tuple(address depositor, address recipient, address exclusiveRelayer, address inputToken, address outputToken, uint256 inputAmount, uint256 outputAmount, uint256 originChainId, uint32 depositId, uint32 fillDeadline, uint32 exclusivityDeadline, bytes message) relayData," +
+              "uint256 chainId," +
+              "uint256 updatedOutputAmount" +
+              ")",
+          ],
+          [input]
+        )
+      );
+    const merkleTreeLegacy = new MerkleTree<V3SlowFill>([legacySlowLeaf], legacyHashFn);
+    const legacyRoot = merkleTreeLegacy.getHexRoot();
+
+    expect(legacyRoot).to.equal(root);
+  });
 });
diff --git a/test/evm/hardhat/SpokePool.Relay.ts b/test/evm/hardhat/SpokePool.Relay.ts
index 2d159e8e9..09ec54a3c 100644
--- a/test/evm/hardhat/SpokePool.Relay.ts
+++ b/test/evm/hardhat/SpokePool.Relay.ts
@@ -12,6 +12,7 @@ import {
   bytes32ToAddress,
   hashNonEmptyMessage,
   toBN,
+  randomBytes32,
 } from "../../../utils/utils";
 import {
   spokePoolFixture,
@@ -21,6 +22,7 @@ import {
   FillType,
   getUpdatedV3DepositSignature,
   getV3RelayHash,
+  getLegacyV3RelayHash,
 } from "./fixtures/SpokePool.Fixture";
 import {
   repaymentChainId,
@@ -89,6 +91,32 @@ describe("SpokePool Relayer Logic", async function () {
         const relayExecution = await getRelayExecutionParams(relayData, destinationChainId);
         expect(await spokePool.fillStatuses(relayExecution.relayHash)).to.equal(FillStatus.Unfilled);
       });
+      // @todo we can remove this after the new spoke pool is upgraded
+      it("relay hash is same pre and post address -> bytes32 upgrade", async function () {
+        const newBytes32Keys = ["depositor", "recipient", "exclusiveRelayer", "inputToken", "outputToken"];
+        const relayDataCopy = { ...relayData, message: randomBytes32() };
+        const legacyRelayData = {
+          ...relayDataCopy,
+          depositor: bytes32ToAddress(relayData.depositor),
+          recipient: bytes32ToAddress(relayData.recipient),
+          exclusiveRelayer: bytes32ToAddress(relayData.exclusiveRelayer),
+          inputToken: bytes32ToAddress(relayData.inputToken),
+          outputToken: bytes32ToAddress(relayData.outputToken),
+        };
+        expect(
+          newBytes32Keys.every(
+            (key) => ethers.utils.hexDataLength(legacyRelayData[key as keyof typeof legacyRelayData] as string) === 20
+          )
+        ).to.be.true;
+        expect(
+          newBytes32Keys.every(
+            (key) => ethers.utils.hexDataLength(relayDataCopy[key as keyof typeof relayDataCopy] as string) === 32
+          )
+        ).to.be.true;
+        const newRelayHash = getV3RelayHash(relayDataCopy, destinationChainId);
+        const oldRelayHash = getLegacyV3RelayHash(legacyRelayData, destinationChainId);
+        expect(newRelayHash).to.equal(oldRelayHash);
+      });
       it("expired fill deadline reverts", async function () {
         const _relay = {
           ...relayData,
diff --git a/test/evm/hardhat/fixtures/SpokePool.Fixture.ts b/test/evm/hardhat/fixtures/SpokePool.Fixture.ts
index 6293c87d9..878015d02 100644
--- a/test/evm/hardhat/fixtures/SpokePool.Fixture.ts
+++ b/test/evm/hardhat/fixtures/SpokePool.Fixture.ts
@@ -191,6 +191,20 @@ export function getV3RelayHash(relayData: V3RelayData, destinationChainId: numbe
   );
 }
 
+// @todo we likely don't need to keep this function around for too long but its useful for making sure that the new relay hash is identical to the
+// legacy one.
+export function getLegacyV3RelayHash(relayData: V3RelayData, destinationChainId: number): string {
+  return ethers.utils.keccak256(
+    defaultAbiCoder.encode(
+      [
+        "tuple(address depositor, address recipient, address exclusiveRelayer, address inputToken, address outputToken, uint256 inputAmount, uint256 outputAmount, uint256 originChainId, uint32 depositId, uint32 fillDeadline, uint32 exclusivityDeadline, bytes message)",
+        "uint256 destinationChainId",
+      ],
+      [relayData, destinationChainId]
+    )
+  );
+}
+
 export function getDepositParams(args: {
   recipient?: string;
   originToken: string;