diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a494ba1..bc33bf0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,10 +1,6 @@
 name: Smart contracts
 
-on:
-  push:
-    branches: [main]
-  pull_request:
-    branches: [main]
+on: ["push", "pull_request"]
 
 jobs:
   build:
diff --git a/contracts/OffsetHelper.sol b/contracts/OffsetHelper.sol
index 3bde11b..0b5d291 100644
--- a/contracts/OffsetHelper.sol
+++ b/contracts/OffsetHelper.sol
@@ -488,11 +488,10 @@ contract OffsetHelper is OffsetHelperStorage {
                 balances[msg.sender][_tco2s[i]] >= _amounts[i],
                 "Insufficient TCO2 balance"
             );
-
-            balances[msg.sender][_tco2s[i]] -= _amounts[i];
-
-            IToucanCarbonOffsets(_tco2s[i]).retire(_amounts[i]);
-
+            if (_amounts[i] > 0) {
+                balances[msg.sender][_tco2s[i]] -= _amounts[i];
+                IToucanCarbonOffsets(_tco2s[i]).retire(_amounts[i]);
+            }
             unchecked {
                 ++i;
             }
diff --git a/test/OffsetHelper.ts b/test/OffsetHelper.ts
index d99bec9..7730d13 100644
--- a/test/OffsetHelper.ts
+++ b/test/OffsetHelper.ts
@@ -11,6 +11,7 @@ import {
 
 import * as hardhatContracts from "../utils/toucanContracts.json";
 import * as poolContract from "../artifacts/contracts/interfaces/IToucanPoolToken.sol/IToucanPoolToken.json";
+import * as carbonOffsetsContract from "../artifacts/contracts/interfaces/IToucanCarbonOffsets.sol/IToucanCarbonOffsets.json";
 import {
   IToucanPoolToken,
   OffsetHelper,
@@ -18,7 +19,7 @@ import {
   Swapper,
   Swapper__factory,
 } from "../typechain";
-import addresses from "../utils/addresses";
+import addresses, { whaleAddresses } from "../utils/addresses";
 import { Contract } from "ethers";
 import { usdcABI, wethABI, wmaticABI } from "../utils/ABIs";
 
@@ -85,13 +86,31 @@ describe("Offset Helper - autoOffset", function () {
       ]
     );
 
-    await Promise.all(
-      addrs.map(async (addr) => {
-        await addr.sendTransaction({
-          to: addr2.address,
-          value: (await addr.getBalance()).sub(parseEther("1.0")),
-        });
-      })
+    // Transfer a large amount of MATIC and NCT to the test account via account impersonation.
+    await network.provider.request({
+      method: "hardhat_impersonateAccount",
+      params: [whaleAddresses.matic],
+    });
+    const maticWhale = ethers.provider.getSigner(whaleAddresses.matic);
+    await maticWhale.sendTransaction({
+      to: addr2.address,
+      value: (await maticWhale.getBalance()).sub(parseEther("1.0")),
+    });
+
+    // Note: The swapper fails when trying to exchange such a large amount of NCT.
+    await network.provider.request({
+      method: "hardhat_impersonateAccount",
+      params: [whaleAddresses.nct],
+    });
+    const addrNctWhale = ethers.provider.getSigner(whaleAddresses.nct);
+    const nctWhaleSigner = new ethers.Contract(
+      addresses.nct,
+      hardhatContracts.contracts.NatureCarbonTonne.abi,
+      addrNctWhale
+    );
+    await nctWhaleSigner.transfer(
+      addr2.address,
+      await nctWhaleSigner.balanceOf(whaleAddresses.nct)
     );
 
     await swapper.swap(addresses.weth, parseEther("20.0"), {
@@ -298,7 +317,7 @@ describe("Offset Helper - autoOffset", function () {
       ).to.be.revertedWith("Insufficient TCO2 balance");
     });
 
-    it("Should retire using an NCT deposit", async function () {
+    it("Should retire using a BCT deposit", async function () {
       await (await bct.approve(offsetHelper.address, parseEther("1.0"))).wait();
 
       await (
@@ -319,6 +338,54 @@ describe("Offset Helper - autoOffset", function () {
 
       await expect(offsetHelper.autoRetire(tco2s, amounts)).to.not.be.reverted;
     });
+
+    it("Should retire using an NCT deposit, even if the first scored TCO2 is not in pool", async function () {
+      const scoredTCO2s = await nct.getScoredTCO2s();
+      const lowestScoredTCO2 = new ethers.Contract(
+        scoredTCO2s[0],
+        carbonOffsetsContract.abi,
+        addr2
+      );
+      const lowestScoredTCO2Balance = await lowestScoredTCO2.balanceOf(
+        addresses.nct
+      );
+
+      // Skip setup if the oldest tco2's balance in the pool is already 0.
+      if (formatEther(lowestScoredTCO2Balance) !== "0.0") {
+        // Setup: If the oldest tco2 balance is non-zero, remove all its tokens from the pool via a redeem.
+        // Ensure that addr2 has enough NCT to redeem all of the lowestScoredTCO2 or setup will fail.
+        expect(await nct.balanceOf(addr2.address)).to.be.above(
+          await lowestScoredTCO2.balanceOf(addresses.nct)
+        );
+
+        await nct.approve(offsetHelper.address, lowestScoredTCO2Balance);
+
+        await offsetHelper.deposit(addresses.nct, lowestScoredTCO2Balance);
+
+        await offsetHelper.autoRedeem(addresses.nct, lowestScoredTCO2Balance);
+      }
+
+      // Ensure the test condition is met.
+      expect(await lowestScoredTCO2.balanceOf(addresses.nct)).to.equal(0);
+
+      await nct.approve(offsetHelper.address, parseEther("1.0"));
+
+      await offsetHelper.deposit(addresses.nct, parseEther("0.0005"));
+
+      const redeemReceipt = await (
+        await offsetHelper.autoRedeem(addresses.nct, parseEther("0.0005"))
+      ).wait();
+
+      if (!redeemReceipt.events) {
+        return;
+      }
+      const tco2s =
+        redeemReceipt.events[redeemReceipt.events.length - 1].args?.tco2s;
+      const amounts =
+        redeemReceipt.events[redeemReceipt.events.length - 1].args?.amounts;
+
+      await expect(offsetHelper.autoRetire(tco2s, amounts)).to.not.be.reverted;
+    });
   });
 
   describe("Testing deposit() and withdraw()", function () {
diff --git a/utils/addresses.ts b/utils/addresses.ts
index d3ed614..d88becf 100644
--- a/utils/addresses.ts
+++ b/utils/addresses.ts
@@ -7,7 +7,11 @@ interface IfcAddresses {
   wmatic: string;
 }
 
-const addresses: IfcAddresses = {
+interface IfcWhaleAddresses {
+  matic: string;
+  nct: string;
+}
+export const addresses: IfcAddresses = {
   myAddress: "0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266",
   bct: "0x2F800Db0fdb5223b3C3f354886d907A671414A7F",
   nct: "0xD838290e877E0188a4A44700463419ED96c16107",
@@ -16,6 +20,11 @@ const addresses: IfcAddresses = {
   wmatic: "0x0d500B1d8E8eF31E21C99d1Db9A6444d3ADf1270",
 };
 
+export const whaleAddresses: IfcWhaleAddresses = {
+  matic: "0xe7804c37c13166fF0b37F5aE0BB07A3aEbb6e245",
+  nct: "0x4b3ebae392e8b90a9b13068e90b27d9c41abc3c8",
+};
+
 export const mumbaiAddresses: IfcAddresses = {
   myAddress: "0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266",
   bct: "0xf2438A14f668b1bbA53408346288f3d7C71c10a1",