2 files changed, 27 insertions, 1 deletions
diff --git a/src/contract_wrappers/exchange_wrapper.ts b/src/contract_wrappers/exchange_wrapper.ts
index 12c2d7396..6726f3eac 100644
--- a/src/contract_wrappers/exchange_wrapper.ts
+++ b/src/contract_wrappers/exchange_wrapper.ts
@@ -1,6 +1,7 @@
 import * as _ from 'lodash';
 import * as BigNumber from 'bignumber.js';
 import promisify = require('es6-promisify');
+import * as Web3 from 'web3';
 import {Web3Wrapper} from '../web3_wrapper';
 import {
     ECSignature,
@@ -26,6 +27,8 @@ import {
     LogErrorContractEventArgs,
     LogFillContractEventArgs,
     LogCancelContractEventArgs,
+    EventCallback,
+    ContractEventArg,
     ExchangeContractByAddress,
     ContractArtifact,
 } from '../types';
@@ -653,14 +656,36 @@ export class ExchangeWrapper extends ContractWrapper {
         return isAuthorized;
     }
     private _wrapEventEmitter(event: ContractEventObj): ContractEventEmitter {
+        const watch = (eventCallback: EventCallback) => {
+            const bignumberWrappingEventCallback = this._getBigNumberWrappingEventCallback(eventCallback);
+            event.watch(bignumberWrappingEventCallback);
+        };
         const zeroExEvent = {
-            watch: event.watch.bind(event),
+            watch,
             stopWatchingAsync: async () => {
                 await promisify(event.stopWatching, event)();
             },
         };
         return zeroExEvent;
     }
+    private _getBigNumberWrappingEventCallback(eventCallback: EventCallback): EventCallback {
+        const bignumberWrappingEventCallback = (err: Error, event: ContractEvent) => {
+            if (_.isNull(err)) {
+                const wrapIfBigNumber = (value: ContractEventArg): ContractEventArg => {
+                    // HACK: The old version of BigNumber used by Web3@0.19.0 does not support the `isBigNumber`
+                    // and checking for a BigNumber instance using `instanceof` does not work either. We therefore
+                    // compare the constructor functions of the possible BigNumber instance and the BigNumber used by
+                    // Web3.
+                    const web3BigNumber = (Web3.prototype as any).BigNumber;
+                    const isWeb3BigNumber = web3BigNumber.toString() === value.constructor.toString();
+                    return isWeb3BigNumber ?  new BigNumber(value) : value;
+                };
+                event.args = _.mapValues(event.args, wrapIfBigNumber);
+            }
+            eventCallback(err, event);
+        };
+        return bignumberWrappingEventCallback;
+    }
     private async _isValidSignatureUsingContractCallAsync(dataHex: string, ecSignature: ECSignature,
                                                           signerAddressHex: string,
                                                           exchangeContractAddress: string): Promise<boolean> {
diff --git a/src/types.ts b/src/types.ts
index 01c22c5ad..8047f4536 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -240,6 +240,7 @@ export interface LogErrorContractEventArgs {
     orderHash: string;
 }
 export type ContractEventArgs = LogFillContractEventArgs|LogCancelContractEventArgs|LogErrorContractEventArgs;
+export type ContractEventArg = string|BigNumber.BigNumber;
 
 export interface Order {
     maker: string;