diff --git a/test/forge/SwapERC20CallParameters.t.sol b/test/forge/SwapERC20CallParameters.t.sol
index 66e5b346..bf9ca41a 100644
--- a/test/forge/SwapERC20CallParameters.t.sol
+++ b/test/forge/SwapERC20CallParameters.t.sol
@@ -244,7 +244,7 @@ contract SwapERC20CallParametersTest is Test, Interop, DeployRouter {
         assertEq(address(router).balance, 0);
     }
 
-    function testV2ExactOutputSingleNativeWithFlatFee() public {
+    function testV2ExactOutputSingleNativeInputWithFlatFee() public {
         MethodParameters memory params = readFixture(json, "._UNISWAP_V2_ETH_FOR_1000_USDC_WITH_FLAT_FEE");
 
         uint256 outputAmount = 1000 * ONE_USDC;
@@ -263,6 +263,27 @@ contract SwapERC20CallParametersTest is Test, Interop, DeployRouter {
         assertEq(address(router).balance, 0);
     }
 
+    function testV2ExactOutputSingleNativeOutputWithFlatFee() public {
+        MethodParameters memory params = readFixture(json, "._UNISWAP_V2_USCD_FOR_10_ETH_WITH_FLAT_FEE");
+
+        deal(address(USDC), from, BALANCE);
+        USDC.approve(address(permit2), BALANCE);
+        permit2.approve(address(USDC), address(router), uint160(BALANCE), uint48(block.timestamp + 1000));
+
+        uint256 outputAmount = 10 ether;
+        uint256 feeAmount = 5 ether;
+
+        assertEq(WETH.balanceOf(FEE_RECIPIENT), 0);
+        uint256 recipientBalanceBefore = RECIPIENT.balance;
+
+        (bool success,) = address(router).call{value: params.value}(params.data);
+        require(success, "call failed");
+        assertGt(RECIPIENT.balance - recipientBalanceBefore, outputAmount); // tiny imprecision with exactOut
+        assertEq(WETH.balanceOf(FEE_RECIPIENT), feeAmount);
+        assertEq(WETH.balanceOf(address(router)), 0);
+        assertEq(address(router).balance, 0);
+    }
+
     function testV2ExactOutputSingleERC20() public {
         MethodParameters memory params = readFixture(json, "._UNISWAP_V2_USDC_FOR_1_ETH");
 
diff --git a/test/forge/interop.json b/test/forge/interop.json
index 407886ec..592fc43e 100644
--- a/test/forge/interop.json
+++ b/test/forge/interop.json
@@ -234,5 +234,13 @@
   "_UNISWAP_V3_1_ETH_FOR_USDC_WITH_FLAT_FEE": {
     "calldata": "0x24856bc30000000000000000000000000000000000000000000000000000000000000040000000000000000000000000000000000000000000000000000000000000008000000000000000000000000000000000000000000000000000000000000000040b000504000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000008000000000000000000000000000000000000000000000000000000000000000e000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000280000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000de0b6b3a7640000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000de0b6b3a76400000000000000000000000000000000000000000000000000000000000044f7ce0000000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002bc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2000bb8a0b86991c6218b36c1d19d4a2e9eb0ce3606eb480000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000060000000000000000000000000a0b86991c6218b36c1d19d4a2e9eb0ce3606eb48000000000000000000000000bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb0000000000000000000000000000000000000000000000000000000002faf0800000000000000000000000000000000000000000000000000000000000000060000000000000000000000000a0b86991c6218b36c1d19d4a2e9eb0ce3606eb48000000000000000000000000aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa0000000000000000000000000000000000000000000000000000000044f7ce00",
     "value": "1000000000000000000"
+  },
+  "_UNISWAP_V2_USCD_FOR_1_ETH_WITH_FLAT_FEE": {
+    "calldata": "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",
+    "value": "0"
+  },
+  "_UNISWAP_V2_USCD_FOR_10_ETH_WITH_FLAT_FEE": {
+    "calldata": "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",
+    "value": "0"
   }
 }
diff --git a/test/uniswapTrades.test.ts b/test/uniswapTrades.test.ts
index 16eadce7..d4037234 100644
--- a/test/uniswapTrades.test.ts
+++ b/test/uniswapTrades.test.ts
@@ -268,6 +268,23 @@ describe('Uniswap', () => {
       expect(methodParameters.value).to.eq(methodParametersV2.value)
     })
 
+    it('encodes a single exactOutput USDC->ETH swap, with a flat fee', async () => {
+      const outputUSDC = utils.parseUnits('15', 18).toString()
+      const trade = new V2Trade(
+        new RouteV2([WETH_USDC_V2], USDC, ETHER),
+        CurrencyAmount.fromRawAmount(ETHER, outputUSDC),
+        TradeType.EXACT_OUTPUT
+      )
+      const feeOptions: FlatFeeOptions = { amount: utils.parseUnits('5', 18), recipient: TEST_FEE_RECIPIENT_ADDRESS }
+      const opts = swapOptions({ flatFee: feeOptions })
+      const methodParameters = SwapRouter.swapERC20CallParameters(buildTrade([trade]), opts)
+      const methodParametersV2 = SwapRouter.swapCallParameters(new UniswapTrade(buildTrade([trade]), opts))
+      registerFixture('_UNISWAP_V2_USCD_FOR_10_ETH_WITH_FLAT_FEE', methodParametersV2)
+      expect(hexToDecimalString(methodParameters.value)).to.equal('0')
+      expect(methodParameters.calldata).to.eq(methodParametersV2.calldata)
+      expect(methodParameters.value).to.eq(methodParametersV2.value)
+    })
+
     it('encodes a single exactOutput USDC->ETH swap', async () => {
       const outputETH = utils.parseEther('1').toString()
       const trade = new V2Trade(