diff --git a/src/api.ts b/src/api.ts
index c2b0245c..ee8eb686 100644
--- a/src/api.ts
+++ b/src/api.ts
@@ -69,7 +69,7 @@ import * as transactionUtils from './transaction/utils'
 import * as schemaValidator from './common/schema-validator'
 import {getServerInfo, getFee} from './common/serverinfo'
 import {clamp} from './ledger/utils'
-import {Instructions} from './transaction/types'
+import {Instructions, Prepare} from './transaction/types'
 
 export type APIOptions = {
   server?: string,
@@ -205,7 +205,8 @@ class RippleAPI extends EventEmitter {
    *
    * You can later submit the transaction with `submit()`.
    */
-  async prepareTransaction(txJSON: object, instructions: Instructions = {}) {
+  async prepareTransaction(txJSON: object, instructions: Instructions = {}):
+    Promise<Prepare> {
     return transactionUtils.prepareTransaction(txJSON, this, instructions)
   }
 
diff --git a/src/transaction/types.ts b/src/transaction/types.ts
index 1724578e..50b87144 100644
--- a/src/transaction/types.ts
+++ b/src/transaction/types.ts
@@ -22,10 +22,10 @@ export type Instructions = {
 export type Prepare = {
   txJSON: string,
   instructions: {
-   fee: string,
-   sequence: number,
-   maxLedgerVersion?: number
- }
+    fee: string,
+    sequence: number,
+    maxLedgerVersion?: number
+  }
 }
 
 export type Submit = {