diff --git a/package.json b/package.json
index f06f21ca57..4743a88c20 100644
--- a/package.json
+++ b/package.json
@@ -11,8 +11,10 @@
     "@actions/core": "^1.10.1",
     "@emotion/react": "^11.11.3",
     "@release-it-plugins/workspaces": "^4.0.0",
+    "@types/chai": "^4.3.16",
     "@typescript-eslint/eslint-plugin": "^5.57.1",
     "@typescript-eslint/parser": "^5.57.1",
+    "chai": "^5.1.1",
     "eslint": "^8.40.0",
     "eslint-config-airbnb": "^19.0.4",
     "eslint-config-airbnb-typescript": "^17.0.0",
diff --git a/packages/orderbook/package.json b/packages/orderbook/package.json
index 37e4ef2583..d6e888a7c2 100644
--- a/packages/orderbook/package.json
+++ b/packages/orderbook/package.json
@@ -15,6 +15,7 @@
     "@swc/jest": "^0.2.24",
     "@typechain/ethers-v5": "^10.2.0",
     "@types/jest": "^29.4.3",
+    "chai": "^5.1.1",
     "dotenv": "^16.0.3",
     "eslint": "^8.40.0",
     "jest": "^29.4.3",
diff --git a/packages/orderbook/src/seaport/fillable-units.spec.ts b/packages/orderbook/src/seaport/fillable-units.spec.ts
new file mode 100644
index 0000000000..b4868e3eb4
--- /dev/null
+++ b/packages/orderbook/src/seaport/fillable-units.spec.ts
@@ -0,0 +1,116 @@
+import { expect } from 'chai';
+import { Fee, Order, ProtocolData } from 'openapi/sdk';
+import { determineFillableUnits } from './fillable-units';
+
+describe('determineFillableUnits', () => {
+  function createOrder(overrides?: Partial<Order>): Order {
+    // Default order object
+    const defaultOrder: Order = {
+      sell: [
+        {
+          type: 'ERC1155',
+          amount: '100',
+          contract_address: '0xEEb7Da6De152597830eD16361633e362A2F59410',
+          token_id: '123',
+        },
+      ],
+      buy: [
+        {
+          type: 'ERC20',
+          amount: '100',
+          contract_address: '0xFFb7Da6De152597830eD16361633e362A2F59411',
+        },
+      ],
+      type: Order.type.LISTING,
+      fill_status: {
+        numerator: '0',
+        denominator: '0',
+      },
+      account_address: '0x1237Da6De152597830eD16361633e362A2F59412',
+      fees: [
+        {
+          type: Fee.type.PROTOCOL,
+          amount: '100',
+          recipient_address: '0x4567Da6De152597830eD16361633e362A2F59413',
+        },
+      ],
+      chain: {
+        id: 'eip155:13473',
+        name: 'imtbl-zkevm-testnet',
+      },
+      created_at: '2024-06-18T06:16:57.902738Z',
+      end_at: '2026-06-18T06:16:14Z',
+      id: '019029fd-cf21-0a33-c77f-e121f5162f22',
+      order_hash: '0xba8ebe0b4ac6f1cc21a2274199b238959aaa0c59e1f2b31a8b7e8a66bf9f9635',
+      protocol_data: {
+        order_type: ProtocolData.order_type.PARTIAL_RESTRICTED,
+        counter: '0',
+        zone_address: '0x1004f9615e79462c711ff05a386bdba91a762822',
+        seaport_address: '0x7d117aa8bd6d31c4fa91722f246388f38ab19482',
+        seaport_version: '1.5',
+      },
+      salt: '0x3217c152146bf9f5',
+      signature: '0xf1522af4913159cdf1172d1c1bd511a3ca617f6c1d0b0ed588b2ce27618a2ac832c31ed4ee6ab2cea8af0efc2ad522468aa1c8c206291f4b343239acfea0a75e1b',
+      start_at: '2024-06-18T06:16:14Z',
+      status: {
+        name: 'ACTIVE',
+      },
+      updated_at: '2024-06-18T06:16:59.006679Z',
+    };
+
+    // Merge the overrides with the default order
+    return { ...defaultOrder, ...overrides };
+  }
+
+  it('should return the remaining fillable units for ERC1155 type when amountToFill is not provided', () => {
+    const orderInput = createOrder({
+      fill_status: {
+        numerator: '40',
+        denominator: '100',
+      },
+    });
+
+    const result = determineFillableUnits(orderInput);
+    expect(result).to.equal('60'); // (100 - 40) * 100 / 100
+  });
+
+  it('should return the original offer amount if order is unfilled i.e numerator or denominator is 0', () => {
+    const order: Order = createOrder();
+
+    const result = determineFillableUnits(order);
+    expect(result).to.equal('100');
+  });
+
+  it('should return amountToFill if provided', () => {
+    const order: Order = createOrder({
+      fill_status: {
+        numerator: '40',
+        denominator: '100',
+      },
+    });
+
+    const amountToFill = '50';
+    const result = determineFillableUnits(order, amountToFill);
+    expect(result).to.equal(amountToFill);
+  });
+
+  it('should return undefined if order type is not ERC1155', () => {
+    const order: Order = createOrder({
+      sell: [
+        {
+          type: 'ERC721',
+          contract_address: '0xEEb7Da6De152597830eD16361633e362A2F59410',
+          token_id: '123',
+        },
+      ],
+      fill_status: {
+        numerator: '0',
+        denominator: '0',
+      },
+    });
+
+    const result = determineFillableUnits(order);
+    // eslint-disable-next-line @typescript-eslint/no-unused-expressions
+    expect(result).to.be.undefined;
+  });
+});
diff --git a/packages/orderbook/src/seaport/fillable-units.ts b/packages/orderbook/src/seaport/fillable-units.ts
new file mode 100644
index 0000000000..47c52aab8b
--- /dev/null
+++ b/packages/orderbook/src/seaport/fillable-units.ts
@@ -0,0 +1,22 @@
+import { Order } from 'openapi/sdk';
+
+export function determineFillableUnits(order: Order, amountToFill?: string): string | undefined {
+  if (order.sell[0].type === 'ERC1155' && !amountToFill) {
+    // fill status is expressed as a ratio
+    const { numerator, denominator } = order.fill_status;
+    const originalOfferAmt = BigInt(order.sell[0].amount);
+
+    if (numerator === '0' || denominator === '0') {
+      return originalOfferAmt.toString();
+    }
+
+    // calculate the remaining amount to fill
+    // remaining = ((denominator - numerator) * originalOfferAmt) / denominator
+    const remaining = ((BigInt(denominator) - BigInt(numerator)) * BigInt(originalOfferAmt))
+        / BigInt(denominator);
+
+    return remaining.toString();
+  }
+
+  return amountToFill;
+}
diff --git a/packages/orderbook/src/seaport/seaport.ts b/packages/orderbook/src/seaport/seaport.ts
index 4437f56574..a52477caa2 100644
--- a/packages/orderbook/src/seaport/seaport.ts
+++ b/packages/orderbook/src/seaport/seaport.ts
@@ -36,6 +36,7 @@ import { getBulkOrderComponentsFromMessage, getOrderComponentsFromMessage } from
 import { SeaportLibFactory } from './seaport-lib-factory';
 import { prepareTransaction } from './transaction';
 import { mapImmutableOrderToSeaportOrderComponents } from './map-to-seaport-order';
+import { determineFillableUnits } from './fillable-units';
 
 export class Seaport {
   constructor(
@@ -175,7 +176,7 @@ export class Seaport {
             parameters: orderComponents,
             signature: order.signature,
           },
-          unitsToFill,
+          unitsToFill: determineFillableUnits(order, unitsToFill),
           extraData,
           tips,
         },
@@ -244,7 +245,7 @@ export class Seaport {
           parameters: orderComponents,
           signature: o.order.signature,
         },
-        unitsToFill: o.unitsToFill,
+        unitsToFill: determineFillableUnits(o.order, o.unitsToFill),
         extraData: o.extraData,
         tips,
       };
diff --git a/tests/func-tests/zkevm/features/order.feature b/tests/func-tests/zkevm/features/order.feature
index 122aece59a..7ce1f65fc9 100644
--- a/tests/func-tests/zkevm/features/order.feature
+++ b/tests/func-tests/zkevm/features/order.feature
@@ -67,3 +67,30 @@ Feature: orderbook
         Then the listing should be of status active
         # Assert only the ERC1155 trade in this scenario
         And 1 trade should be available
+
+    Scenario: create and fully fill a ERC1155 listing without an explicit fulfill amount
+        Given I have a funded offerer account
+        And the offerer account has 100 ERC1155 tokens
+        And I have a funded fulfiller account
+        When I create a listing to sell 100 ERC1155 tokens
+        Then the listing should be of status active
+        When I fulfill the listing to buy tokens
+        Then the listing should be of status filled
+        And 100 ERC1155 tokens should be transferred to the fulfiller
+        And 1 trade should be available
+
+    Scenario: create and partially fill a ERC1155 listing, second fill without explicit amount
+        Given I have a funded offerer account
+        And the offerer account has 100 ERC1155 tokens
+        And I have a funded fulfiller account
+        When I create a listing to sell 100 ERC1155 tokens
+        Then the listing should be of status active
+        When I fulfill the listing to buy 90 tokens
+        Then the listing should be of status active
+        And 90 ERC1155 tokens should be transferred to the fulfiller
+        And 1 trade should be available
+        When I fulfill the listing to buy tokens
+        Then the listing should be of status filled
+        # Checks for the total amount of tokens transferred - 100 = 90 from first fulfilment + 10 from second fulfilment
+        And 100 ERC1155 tokens should be transferred to the fulfiller
+        And 2 trades should be available
\ No newline at end of file
diff --git a/tests/func-tests/zkevm/step-definitions/order.steps.ts b/tests/func-tests/zkevm/step-definitions/order.steps.ts
index 4c94cffa84..16a1b46727 100644
--- a/tests/func-tests/zkevm/step-definitions/order.steps.ts
+++ b/tests/func-tests/zkevm/step-definitions/order.steps.ts
@@ -13,7 +13,7 @@ import {
   givenIHaveAFundedOffererAccount, thenTheListingShouldBeOfStatus,
   whenICreateAListing, whenIFulfillTheListingToBuy, andERC1155TokensShouldBeTransferredToTheFulfiller,
   thenTheListingsShouldBeOfStatus,
-  whenIFulfillBulkListings,
+  whenIFulfillBulkListings, whenIFulfillTheListingToBuyWithoutExplicitFulfillmentAmt,
   whenICreateABulkListing,
 } from './shared';
 
@@ -257,4 +257,89 @@ defineFeature(feature, (test) => {
 
     andTradeShouldBeAvailable(and, sdk, fulfiller, getERC1155ListingId);
   }, 120_000);
+
+  test('create and fully fill a ERC1155 listing without an explicit fulfill amount', ({
+    given,
+    when,
+    then,
+    and,
+  }) => {
+    const offerer = new Wallet(Wallet.createRandom().privateKey, provider);
+    const fulfiller = new Wallet(Wallet.createRandom().privateKey, provider);
+    const testTokenId = getRandomTokenId();
+
+    let listingId: string = '';
+
+    // these callback functions are required to update / retrieve test level state variables from shared steps.
+    const setListingId = (id: string) => {
+      listingId = id;
+    };
+
+    const getListingId = () => listingId;
+    givenIHaveAFundedOffererAccount(given, bankerWallet, offerer);
+
+    andTheOffererAccountHasERC1155Tokens(and, bankerWallet, offerer, erc1155ContractAddress, testTokenId);
+
+    andIHaveAFundedFulfillerAccount(and, bankerWallet, fulfiller);
+
+    whenICreateAListing(when, sdk, offerer, erc1155ContractAddress, testTokenId, setListingId);
+
+    thenTheListingShouldBeOfStatus(then, sdk, getListingId);
+
+    whenIFulfillTheListingToBuyWithoutExplicitFulfillmentAmt(when, sdk, fulfiller, getListingId);
+
+    thenTheListingShouldBeOfStatus(then, sdk, getListingId);
+
+    // eslint-disable-next-line max-len
+    andERC1155TokensShouldBeTransferredToTheFulfiller(and, bankerWallet, erc1155ContractAddress, testTokenId, fulfiller);
+
+    andTradeShouldBeAvailable(and, sdk, fulfiller, getListingId);
+  }, 120_000);
+
+  test('create and partially fill a ERC1155 listing, second fill without explicit amount', ({
+    given,
+    when,
+    then,
+    and,
+  }) => {
+    const offerer = new Wallet(Wallet.createRandom().privateKey, provider);
+    const fulfiller = new Wallet(Wallet.createRandom().privateKey, provider);
+    const testTokenId = getRandomTokenId();
+
+    let listingId: string = '';
+
+    // these callback functions are required to update / retrieve test level state variables from shared steps.
+    const setListingId = (id: string) => {
+      listingId = id;
+    };
+
+    const getListingId = () => listingId;
+    givenIHaveAFundedOffererAccount(given, bankerWallet, offerer);
+
+    andTheOffererAccountHasERC1155Tokens(and, bankerWallet, offerer, erc1155ContractAddress, testTokenId);
+
+    andIHaveAFundedFulfillerAccount(and, bankerWallet, fulfiller);
+
+    whenICreateAListing(when, sdk, offerer, erc1155ContractAddress, testTokenId, setListingId);
+
+    thenTheListingShouldBeOfStatus(then, sdk, getListingId);
+
+    whenIFulfillTheListingToBuy(when, sdk, fulfiller, getListingId);
+
+    thenTheListingShouldBeOfStatus(then, sdk, getListingId);
+
+    // eslint-disable-next-line max-len
+    andERC1155TokensShouldBeTransferredToTheFulfiller(and, bankerWallet, erc1155ContractAddress, testTokenId, fulfiller);
+
+    andTradeShouldBeAvailable(and, sdk, fulfiller, getListingId);
+
+    whenIFulfillTheListingToBuyWithoutExplicitFulfillmentAmt(when, sdk, fulfiller, getListingId);
+
+    thenTheListingShouldBeOfStatus(then, sdk, getListingId);
+
+    // eslint-disable-next-line max-len
+    andERC1155TokensShouldBeTransferredToTheFulfiller(and, bankerWallet, erc1155ContractAddress, testTokenId, fulfiller);
+
+    andTradeShouldBeAvailable(and, sdk, fulfiller, getListingId);
+  }, 120_000);
 });
diff --git a/tests/func-tests/zkevm/step-definitions/shared.ts b/tests/func-tests/zkevm/step-definitions/shared.ts
index b75e36d338..9380e4c31c 100644
--- a/tests/func-tests/zkevm/step-definitions/shared.ts
+++ b/tests/func-tests/zkevm/step-definitions/shared.ts
@@ -217,6 +217,18 @@ export const whenIFulfillTheListingToBuy = (
   });
 };
 
+export const whenIFulfillTheListingToBuyWithoutExplicitFulfillmentAmt = (
+  when: DefineStepFunction,
+  sdk: orderbook.Orderbook,
+  fulfiller: Wallet,
+  getListingId: () => string,
+) => {
+  when(/^I fulfill the listing to buy tokens?$/, async () => {
+    const listingId = getListingId();
+    await fulfillListing(sdk, listingId, fulfiller);
+  });
+};
+
 export const whenIFulfillBulkListings = (
   when: DefineStepFunction,
   sdk: orderbook.Orderbook,
diff --git a/tests/func-tests/zkevm/yarn.lock b/tests/func-tests/zkevm/yarn.lock
index d424a29198..dc83a5e3cb 100644
--- a/tests/func-tests/zkevm/yarn.lock
+++ b/tests/func-tests/zkevm/yarn.lock
@@ -1105,7 +1105,7 @@ __metadata:
 
 "@imtbl/sdk@file:../../../sdk::locator=func-tests-imx%40workspace%3A.":
   version: 0.0.0
-  resolution: "@imtbl/sdk@file:../../../sdk#../../../sdk::hash=972221&locator=func-tests-imx%40workspace%3A."
+  resolution: "@imtbl/sdk@file:../../../sdk#../../../sdk::hash=27c191&locator=func-tests-imx%40workspace%3A."
   dependencies:
     "@0xsequence/abi": ^1.4.3
     "@0xsequence/core": ^1.4.3
@@ -1162,7 +1162,7 @@ __metadata:
       optional: true
     prisma:
       optional: true
-  checksum: ff9a304bbe822028dd13295de657af04bcc19b4b5b0fd98fa49f624f05ece052041caaf690d33a495e7485dce9400c1eab48df0a3923b48534742697590f3364
+  checksum: ece1b9f5eb071b687eb942e1885e5718dbec44ec6bd656b1dd7bffcee58f30f46d4dbc48ee0149a00d4b99ddb20af07c990f92e435b914e3ce39764bfba8072c
   languageName: node
   linkType: hard
 
diff --git a/yarn.lock b/yarn.lock
index cbf52672b4..702b6185c1 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3748,6 +3748,7 @@ __metadata:
     "@typechain/ethers-v5": ^10.2.0
     "@types/jest": ^29.4.3
     axios: ^1.6.5
+    chai: ^5.1.1
     dotenv: ^16.0.3
     eslint: ^8.40.0
     ethers: ^5.7.2
@@ -9199,6 +9200,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@types/chai@npm:^4.3.16":
+  version: 4.3.16
+  resolution: "@types/chai@npm:4.3.16"
+  checksum: bb5f52d1b70534ed8b4bf74bd248add003ffe1156303802ea367331607c06b494da885ffbc2b674a66b4f90c9ee88759790a5f243879f6759f124f22328f5e95
+  languageName: node
+  linkType: hard
+
 "@types/connect-history-api-fallback@npm:^1.3.5":
   version: 1.5.0
   resolution: "@types/connect-history-api-fallback@npm:1.5.0"
@@ -11886,6 +11894,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"assertion-error@npm:^2.0.1":
+  version: 2.0.1
+  resolution: "assertion-error@npm:2.0.1"
+  checksum: a0789dd882211b87116e81e2648ccb7f60340b34f19877dd020b39ebb4714e475eb943e14ba3e22201c221ef6645b7bfe10297e76b6ac95b48a9898c1211ce66
+  languageName: node
+  linkType: hard
+
 "ast-types-flow@npm:^0.0.7":
   version: 0.0.7
   resolution: "ast-types-flow@npm:0.0.7"
@@ -13092,6 +13107,19 @@ __metadata:
   languageName: node
   linkType: hard
 
+"chai@npm:^5.1.1":
+  version: 5.1.1
+  resolution: "chai@npm:5.1.1"
+  dependencies:
+    assertion-error: ^2.0.1
+    check-error: ^2.1.1
+    deep-eql: ^5.0.1
+    loupe: ^3.1.0
+    pathval: ^2.0.0
+  checksum: 1e0a5e1b5febdfa8ceb97b9aff608286861ecb86533863119b2f39f07c08fb59f3c1791ab554947f009b9d71d509b9e4e734fb12133cb81f231c2c2ee7c1e738
+  languageName: node
+  linkType: hard
+
 "chalk@npm:4.1.1, chalk@npm:^4.1.1":
   version: 4.1.1
   resolution: "chalk@npm:4.1.1"
@@ -13168,6 +13196,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"check-error@npm:^2.1.1":
+  version: 2.1.1
+  resolution: "check-error@npm:2.1.1"
+  checksum: d785ed17b1d4a4796b6e75c765a9a290098cf52ff9728ce0756e8ffd4293d2e419dd30c67200aee34202463b474306913f2fcfaf1890641026d9fc6966fea27a
+  languageName: node
+  linkType: hard
+
 "check-more-types@npm:^2.24.0":
   version: 2.24.0
   resolution: "check-more-types@npm:2.24.0"
@@ -14632,6 +14667,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"deep-eql@npm:^5.0.1":
+  version: 5.0.2
+  resolution: "deep-eql@npm:5.0.2"
+  checksum: 6aaaadb4c19cbce42e26b2bbe5bd92875f599d2602635dc97f0294bae48da79e89470aedee05f449e0ca8c65e9fd7e7872624d1933a1db02713d99c2ca8d1f24
+  languageName: node
+  linkType: hard
+
 "deep-equal@npm:^2.0.5":
   version: 2.2.2
   resolution: "deep-equal@npm:2.2.2"
@@ -17432,6 +17474,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"get-func-name@npm:^2.0.1":
+  version: 2.0.2
+  resolution: "get-func-name@npm:2.0.2"
+  checksum: 3f62f4c23647de9d46e6f76d2b3eafe58933a9b3830c60669e4180d6c601ce1b4aa310ba8366143f55e52b139f992087a9f0647274e8745621fa2af7e0acf13b
+  languageName: node
+  linkType: hard
+
 "get-intrinsic@npm:^1.0.2, get-intrinsic@npm:^1.1.1, get-intrinsic@npm:^1.1.3, get-intrinsic@npm:^1.2.0, get-intrinsic@npm:^1.2.1":
   version: 1.2.1
   resolution: "get-intrinsic@npm:1.2.1"
@@ -21549,6 +21598,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"loupe@npm:^3.1.0":
+  version: 3.1.1
+  resolution: "loupe@npm:3.1.1"
+  dependencies:
+    get-func-name: ^2.0.1
+  checksum: c7efa6bc6d71f25ca03eb13c9a069e35ed86799e308ca27a7a3eff8cdf9500e7c22d1f2411468d154a8e960e91e5e685e0c6c83e96db748f177c1adf30811153
+  languageName: node
+  linkType: hard
+
 "lower-case@npm:^2.0.2":
   version: 2.0.2
   resolution: "lower-case@npm:2.0.2"
@@ -23568,6 +23626,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"pathval@npm:^2.0.0":
+  version: 2.0.0
+  resolution: "pathval@npm:2.0.0"
+  checksum: 682b6a6289de7990909effef7dae9aa7bb6218c0426727bccf66a35b34e7bfbc65615270c5e44e3c9557a5cb44b1b9ef47fc3cb18bce6ad3ba92bcd28467ed7d
+  languageName: node
+  linkType: hard
+
 "pbkdf2@npm:^3.0.17, pbkdf2@npm:^3.0.3":
   version: 3.1.2
   resolution: "pbkdf2@npm:3.1.2"
@@ -28597,8 +28662,10 @@ __metadata:
     "@actions/core": ^1.10.1
     "@emotion/react": ^11.11.3
     "@release-it-plugins/workspaces": ^4.0.0
+    "@types/chai": ^4.3.16
     "@typescript-eslint/eslint-plugin": ^5.57.1
     "@typescript-eslint/parser": ^5.57.1
+    chai: ^5.1.1
     eslint: ^8.40.0
     eslint-config-airbnb: ^19.0.4
     eslint-config-airbnb-typescript: ^17.0.0