diff --git a/foundry/src/uniswap_x/UniswapXFiller.sol b/foundry/src/uniswap_x/UniswapXFiller.sol
index 1156c31..bc5a3f9 100644
--- a/foundry/src/uniswap_x/UniswapXFiller.sol
+++ b/foundry/src/uniswap_x/UniswapXFiller.sol
@@ -9,6 +9,7 @@ import {
 } from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
 import "@openzeppelin/contracts/access/AccessControl.sol";
 import "@openzeppelin/contracts/utils/Address.sol";
+import {TychoRouter} from "../TychoRouter.sol";
 
 error UniswapXFiller__AddressZero();
 error UniswapXFiller__BatchExecutionNotSupported();
@@ -58,12 +59,34 @@ contract UniswapXFiller is AccessControl, IReactorCallback {
 
         ResolvedOrder memory order = resolvedOrders[0];
 
+        (
+            bool tokenInApprovalNeeded,
+            bool tokenOutApprovalNeeded,
+            bytes memory tychoCalldata
+        ) = abi.decode(callbackData, (bool, bool, bytes));
+
+        // The TychoRouter will take the input tokens from the filler
+        if (tokenInApprovalNeeded) {
+            // TODO only if ERC20
+            IERC20(order.input.token).forceApprove(
+                tychoRouter, order.input.maxAmount
+            );
+        } else {
+            // The filler will manually transfer into the TychoRouter
+            // Note: We are using the balance of our filler instead of the order
+            // input amount to avoid having to do a decay calculation in the filler.
+            IERC20 inputToken = IERC20(order.input.token);
+            inputToken.transfer(
+                tychoRouter, inputToken.balanceOf(address(this))
+            );
+        }
+
         // TODO properly handle native in and out tokens
         uint256 ethValue = 0;
 
         // slither-disable-next-line low-level-calls
         (bool success, bytes memory result) =
-            tychoRouter.call{value: ethValue}(callbackData);
+            tychoRouter.call{value: ethValue}(tychoCalldata);
 
         if (!success) {
             revert(
@@ -75,10 +98,13 @@ contract UniswapXFiller is AccessControl, IReactorCallback {
             );
         }
 
-        // Multiple outputs are possible when taking fees - but token itself should
-        // not change.
-        IERC20 token = IERC20(order.outputs[0].token);
-        token.forceApprove(address(reactor), type(uint256).max);
+        if (tokenOutApprovalNeeded) {
+            // Multiple outputs are possible when taking fees - but token itself should
+            // not change.
+            // TODO only if ERC20
+            IERC20 token = IERC20(order.outputs[0].token);
+            token.forceApprove(address(reactor), type(uint256).max);
+        }
     }
 
     /**
diff --git a/foundry/test/uniswap_x/UniswapXFiller.t.sol b/foundry/test/uniswap_x/UniswapXFiller.t.sol
index 8102e4f..49f9e90 100644
--- a/foundry/test/uniswap_x/UniswapXFiller.t.sol
+++ b/foundry/test/uniswap_x/UniswapXFiller.t.sol
@@ -55,7 +55,7 @@ contract UniswapXFillerTest is Test, TychoRouterTestSetup {
         bytes memory swap =
             encodeSingleSwap(address(usv2Executor), protocolData);
 
-        bytes memory callbackData = abi.encodeWithSelector(
+        bytes memory tychoRouterData = abi.encodeWithSelector(
             tychoRouter.singleSwap.selector,
             amountIn,
             WETH_ADDR,
@@ -68,6 +68,8 @@ contract UniswapXFillerTest is Test, TychoRouterTestSetup {
             swap
         );
 
+        bytes memory callbackData = abi.encode(true, true, tychoRouterData);
+
         deal(WETH_ADDR, address(filler), amountIn);
         vm.startPrank(address(filler));
         IERC20(WETH_ADDR).approve(tychoRouterAddr, amountIn);
@@ -76,11 +78,11 @@ contract UniswapXFillerTest is Test, TychoRouterTestSetup {
         OutputToken[] memory outputs = new OutputToken[](1);
         outputs[0] = OutputToken({
             token: address(DAI_ADDR),
-            // Irrelevant fields - we only need the token address for approval
             amount: 1847751195973566072891,
             recipient: BOB
         });
-        // All irrelevant fields for this test - we only need the output token address
+        // Mostly irrelevant fields for this test - we only need token input and outputs
+        // info for the sake of testing.
         orders[0] = ResolvedOrder({
             info: OrderInfo({
                 reactor: address(0),
@@ -90,7 +92,12 @@ contract UniswapXFillerTest is Test, TychoRouterTestSetup {
                 additionalValidationContract: address(0),
                 additionalValidationData: ""
             }),
-            input: InputToken({token: address(WETH_ADDR), amount: 0, maxAmount: 0}),
+            input: InputToken({
+                token: address(WETH_ADDR),
+                amount: amountIn,
+                // We need the proper maxAmount for our approval to work
+                maxAmount: amountIn
+            }),
             outputs: outputs,
             sig: "",
             hash: ""
@@ -133,7 +140,7 @@ contract UniswapXFillerTest is Test, TychoRouterTestSetup {
         bytes memory swap =
             encodeSingleSwap(address(usv2Executor), protocolData);
 
-        bytes memory callbackData = abi.encodeWithSelector(
+        bytes memory tychoRouterData = abi.encodeWithSelector(
             tychoRouter.singleSwap.selector,
             amountIn,
             WBTC_ADDR,
@@ -146,6 +153,12 @@ contract UniswapXFillerTest is Test, TychoRouterTestSetup {
             swap
         );
 
+        bytes memory callbackData = abi.encode(
+            true, // tokenIn approval needed
+            true, // tokenOut approval needed
+            tychoRouterData
+        );
+
         vm.startPrank(address(filler));
         IERC20(WBTC_ADDR).approve(tychoRouterAddr, amountIn);
         vm.stopPrank();