diff --git a/packages/orderbook/src/seaport/seaport.test.ts b/packages/orderbook/src/seaport/seaport.test.ts
index 0c5ad078b4..31cff6e0ed 100644
--- a/packages/orderbook/src/seaport/seaport.test.ts
+++ b/packages/orderbook/src/seaport/seaport.test.ts
@@ -420,6 +420,11 @@ describe('Seaport', () => {
         const mockedSeaportJs = mock(SeaportLib);
         const mockedSeaportLibFactory = mock(SeaportLibFactory);
         const mockedProvider = mock(providers.JsonRpcProvider);
+        when(mockedProvider.getNetwork()).thenReturn(
+          Promise.resolve({
+            chainId: 0,
+          } as any),
+        );
 
         const exchangeTransactionMethods = mock<TransactionMethods<boolean>>();
         const exchangeAction = mock<ExchangeAction<any>>();
diff --git a/packages/orderbook/src/seaport/seaport.ts b/packages/orderbook/src/seaport/seaport.ts
index 0d60572a46..e15a8b8855 100644
--- a/packages/orderbook/src/seaport/seaport.ts
+++ b/packages/orderbook/src/seaport/seaport.ts
@@ -67,7 +67,10 @@ export class Seaport {
       listingActions.push({
         type: ActionType.TRANSACTION,
         purpose: TransactionPurpose.APPROVAL,
-        buildTransaction: prepareTransaction(approvalAction.transactionMethods),
+        buildTransaction: prepareTransaction(
+          approvalAction.transactionMethods,
+          (await this.provider.getNetwork()).chainId,
+        ),
       });
     }
 
@@ -126,7 +129,10 @@ export class Seaport {
     if (approvalAction) {
       fulfillmentActions.push({
         type: ActionType.TRANSACTION,
-        buildTransaction: prepareTransaction(approvalAction.transactionMethods),
+        buildTransaction: prepareTransaction(
+          approvalAction.transactionMethods,
+          (await this.provider.getNetwork()).chainId,
+        ),
         purpose: TransactionPurpose.APPROVAL,
       });
     }
@@ -141,7 +147,10 @@ export class Seaport {
 
     fulfillmentActions.push({
       type: ActionType.TRANSACTION,
-      buildTransaction: prepareTransaction(fulfilOrderAction.transactionMethods),
+      buildTransaction: prepareTransaction(
+        fulfilOrderAction.transactionMethods,
+        (await this.provider.getNetwork()).chainId,
+      ),
       purpose: TransactionPurpose.FULFILL_ORDER,
     });
 
@@ -186,7 +195,10 @@ export class Seaport {
     if (approvalAction) {
       fulfillmentActions.push({
         type: ActionType.TRANSACTION,
-        buildTransaction: prepareTransaction(approvalAction.transactionMethods),
+        buildTransaction: prepareTransaction(
+          approvalAction.transactionMethods,
+          (await this.provider.getNetwork()).chainId,
+        ),
         purpose: TransactionPurpose.APPROVAL,
       });
     }
@@ -201,7 +213,10 @@ export class Seaport {
 
     fulfillmentActions.push({
       type: ActionType.TRANSACTION,
-      buildTransaction: prepareTransaction(fulfilOrderAction.transactionMethods),
+      buildTransaction: prepareTransaction(
+        fulfilOrderAction.transactionMethods,
+        (await this.provider.getNetwork()).chainId,
+      ),
       purpose: TransactionPurpose.FULFILL_ORDER,
     });
 
@@ -224,7 +239,10 @@ export class Seaport {
 
     return {
       type: ActionType.TRANSACTION,
-      buildTransaction: prepareTransaction(cancellationTransaction),
+      buildTransaction: prepareTransaction(
+        cancellationTransaction,
+        (await this.provider.getNetwork()).chainId,
+      ),
       purpose: TransactionPurpose.CANCEL,
     };
   }
diff --git a/packages/orderbook/src/seaport/transaction.ts b/packages/orderbook/src/seaport/transaction.ts
index f552d45b42..68497aab68 100644
--- a/packages/orderbook/src/seaport/transaction.ts
+++ b/packages/orderbook/src/seaport/transaction.ts
@@ -5,12 +5,15 @@ import { TransactionBuilder } from 'types';
 // This can always be overwritten by the user signing the transaction
 export function prepareTransaction(
   transactionMethods: TransactionMethods,
+  // chainId is required for EIP155
+  chainId: number,
 ): TransactionBuilder {
   return async () => {
     const transaction = await transactionMethods.buildTransaction();
     transaction.gasLimit = await transactionMethods.estimateGas();
     transaction.gasLimit = transaction.gasLimit
       .add(transaction.gasLimit.div(5));
+    transaction.chainId = chainId;
 
     return transaction;
   };