diff --git a/src/orders/erc20Fulfillment.ts b/src/orders/erc20Fulfillment.ts
index 8050a9f82..68937d693 100644
--- a/src/orders/erc20Fulfillment.ts
+++ b/src/orders/erc20Fulfillment.ts
@@ -171,7 +171,13 @@ export function getErc20Payment(inputData: unknown): Erc20Payment | null {
     return null
   }
 
-  if ("basicOrderParameters" in inputData) {
+  // The fulfillment API serializes a decoded fulfillBasicOrder call as a single
+  // `parameters` struct. Older hand-written SDK types called this
+  // `basicOrderParameters`, so accept that shape as a compatibility fallback.
+  if (isRecord(inputData.parameters)) {
+    return basicOrderErc20Payment(inputData.parameters)
+  }
+  if (isRecord(inputData.basicOrderParameters)) {
     return basicOrderErc20Payment(inputData.basicOrderParameters)
   }
 
@@ -200,8 +206,13 @@ export function getFulfillerConduitKey(inputData: unknown): string | null {
   if (typeof direct === "string") {
     return direct
   }
-  if (isRecord(inputData.basicOrderParameters)) {
-    const fromBasicOrder = inputData.basicOrderParameters.fulfillerConduitKey
+  const basicOrderParameters = isRecord(inputData.parameters)
+    ? inputData.parameters
+    : isRecord(inputData.basicOrderParameters)
+      ? inputData.basicOrderParameters
+      : null
+  if (basicOrderParameters) {
+    const fromBasicOrder = basicOrderParameters.fulfillerConduitKey
     if (typeof fromBasicOrder === "string") {
       return fromBasicOrder
     }
diff --git a/test/orders/erc20Fulfillment.spec.ts b/test/orders/erc20Fulfillment.spec.ts
index 6107a4d14..0c48ac2d9 100644
--- a/test/orders/erc20Fulfillment.spec.ts
+++ b/test/orders/erc20Fulfillment.spec.ts
@@ -69,7 +69,9 @@ function advancedOrderInput(consideration: unknown[]) {
 /** basicOrderType 8 is route 2, ERC20_TO_ERC721: the fulfiller pays with ERC20. */
 function basicOrderInput(overrides: Record<string, unknown> = {}) {
   return {
-    basicOrderParameters: {
+    // The fulfillment API serializes fulfillBasicOrder's single decoded struct
+    // under `parameters`, matching the shape consumed by FulfillmentManager.
+    parameters: {
       considerationToken: USDG,
       considerationIdentifier: "0",
       considerationAmount: "360000000",
@@ -170,7 +172,7 @@ describe("getErc20Payment: advanced and standard orders", () => {
 })
 
 describe("getErc20Payment: basic orders", () => {
-  test("sums considerationAmount and additionalRecipients for an ERC20 route", () => {
+  test("sums considerationAmount and additionalRecipients from the API parameters shape", () => {
     expect(getErc20Payment(basicOrderInput())).toEqual({
       token: USDG,
       amount: 369000000n,
@@ -252,7 +254,7 @@ describe("getFulfillerConduitKey", () => {
     expect(getFulfillerConduitKey(advancedOrderInput([]))).toBe(CONDUIT_KEY)
   })
 
-  test("reads the key nested in basicOrderParameters", () => {
+  test("reads the key nested in the basic-order API parameters", () => {
     expect(getFulfillerConduitKey(basicOrderInput())).toBe(CONDUIT_KEY)
   })