diff --git a/src/fund/utils/subscribeToWindowMessage.test.ts b/src/fund/utils/subscribeToWindowMessage.test.ts
index 2f3be349dc..fd0b99db26 100644
--- a/src/fund/utils/subscribeToWindowMessage.test.ts
+++ b/src/fund/utils/subscribeToWindowMessage.test.ts
@@ -26,10 +26,12 @@ describe('subscribeToWindowMessage', () => {
       allowedOrigin: DEFAULT_ORIGIN,
     });
 
-    const event = mockMessageEvent({
-      eventName: MessageCodes.Event,
-      data: { key: 'value' },
-    });
+    const event = mockMessageEvent(
+      JSON.stringify({
+        eventName: MessageCodes.Event,
+        data: { key: 'value' },
+      }),
+    );
     window.dispatchEvent(event);
 
     //wait for the async code to run
@@ -45,10 +47,12 @@ describe('subscribeToWindowMessage', () => {
       allowedOrigin: 'https://not.allowed.origin',
     });
 
-    const event = mockMessageEvent({
-      eventName: MessageCodes.Event,
-      data: { key: 'value' },
-    });
+    const event = mockMessageEvent(
+      JSON.stringify({
+        eventName: MessageCodes.Event,
+        data: { key: 'value' },
+      }),
+    );
     window.dispatchEvent(event);
 
     //wait for the async code to run
@@ -66,10 +70,12 @@ describe('subscribeToWindowMessage', () => {
       onValidateOrigin,
     });
 
-    const event = mockMessageEvent({
-      eventName: MessageCodes.Event,
-      data: { key: 'value' },
-    });
+    const event = mockMessageEvent(
+      JSON.stringify({
+        eventName: MessageCodes.Event,
+        data: { key: 'value' },
+      }),
+    );
     window.dispatchEvent(event);
 
     //wait for the async code to run
@@ -88,10 +94,12 @@ describe('subscribeToWindowMessage', () => {
       onValidateOrigin,
     });
 
-    const event = mockMessageEvent({
-      eventName: MessageCodes.Event,
-      data: { key: 'value' },
-    });
+    const event = mockMessageEvent(
+      JSON.stringify({
+        eventName: MessageCodes.Event,
+        data: { key: 'value' },
+      }),
+    );
     window.dispatchEvent(event);
 
     //wait for the async code to run
@@ -108,10 +116,12 @@ describe('subscribeToWindowMessage', () => {
       allowedOrigin: DEFAULT_ORIGIN,
     });
 
-    const event = mockMessageEvent({
-      eventName: 'not-event',
-      data: { key: 'value' },
-    });
+    const event = mockMessageEvent(
+      JSON.stringify({
+        eventName: 'not-event',
+        data: { key: 'value' },
+      }),
+    );
     window.dispatchEvent(event);
 
     //wait for the async code to run
diff --git a/src/fund/utils/subscribeToWindowMessage.ts b/src/fund/utils/subscribeToWindowMessage.ts
index 55edd8edaf..a0399f1090 100644
--- a/src/fund/utils/subscribeToWindowMessage.ts
+++ b/src/fund/utils/subscribeToWindowMessage.ts
@@ -10,15 +10,8 @@ export enum MessageCodes {
   Event = 'event',
 }
 
-type MessageCode = `${MessageCodes}`;
-
 type MessageData = JsonObject;
 
-type PostMessageData = {
-  eventName: MessageCode;
-  data?: MessageData;
-};
-
 /**
  * Subscribes to a message from the parent window.
  * @param messageCode A message code to subscribe to.
@@ -36,12 +29,12 @@ export function subscribeToWindowMessage({
   allowedOrigin: string;
   onValidateOrigin?: (origin: string) => Promise<boolean>;
 }) {
-  const handleMessage = (event: MessageEvent<PostMessageData>) => {
+  const handleMessage = (event: MessageEvent<string>) => {
     if (!isAllowedOrigin({ event, allowedOrigin })) {
       return;
     }
 
-    const { eventName, data } = event.data;
+    const { eventName, data } = JSON.parse(event.data);
 
     if (eventName === 'event') {
       (async () => {