diff --git a/src/middleware/createRpcWarningMiddleware.test.ts b/src/middleware/createRpcWarningMiddleware.test.ts
index d3bdf120..90ffb112 100644
--- a/src/middleware/createRpcWarningMiddleware.test.ts
+++ b/src/middleware/createRpcWarningMiddleware.test.ts
@@ -109,7 +109,7 @@ describe('createRpcWarningMiddleware', () => {
         method,
       })) as JsonRpcFailure;
 
-      expect(result.error.message).toBe('Failure!');
+      expect(result.error.message).toBe('Internal JSON-RPC error.');
     });
   });
 
@@ -159,7 +159,7 @@ describe('createRpcWarningMiddleware', () => {
         params,
       })) as JsonRpcFailure;
 
-      expect(result.error.message).toBe('Failure!');
+      expect(result.error.message).toBe('Internal JSON-RPC error.');
     });
   });
 });
diff --git a/test/mocks/MockConnectionStream.ts b/test/mocks/MockConnectionStream.ts
index d421ac48..8972fab6 100644
--- a/test/mocks/MockConnectionStream.ts
+++ b/test/mocks/MockConnectionStream.ts
@@ -1,5 +1,7 @@
 import {
+  Json,
   JsonRpcNotification,
+  JsonRpcParams,
   JsonRpcRequest,
   JsonRpcResponse,
 } from '@metamask/utils';
@@ -71,7 +73,7 @@ export class MockConnectionStream extends Duplex {
    * @param substream - The substream this reply is included in.
    * @param message - The JSON RPC response.
    */
-  reply(substream: string, message: JsonRpcResponse) {
+  reply(substream: string, message: JsonRpcResponse<Json>) {
     this.push({ name: substream, data: message });
   }
 
@@ -81,7 +83,7 @@ export class MockConnectionStream extends Duplex {
    * @param substream - The substream this notification is included in.
    * @param message - The JSON RPC notification.
    */
-  notify(substream: string, message: JsonRpcNotification<unknown>) {
+  notify(substream: string, message: JsonRpcNotification<JsonRpcParams>) {
     this.push({ name: substream, data: message });
   }
 }
diff --git a/test/mocks/MockPort.ts b/test/mocks/MockPort.ts
index 5c22a542..6e916170 100644
--- a/test/mocks/MockPort.ts
+++ b/test/mocks/MockPort.ts
@@ -1,4 +1,5 @@
 import {
+  Json,
   JsonRpcNotification,
   JsonRpcRequest,
   JsonRpcResponse,
@@ -77,7 +78,7 @@ export class MockPort {
    * @param substream - The substream this reply is included in.
    * @param message - The JSON RPC response.
    */
-  reply(substream: string, message: JsonRpcResponse) {
+  reply(substream: string, message: JsonRpcResponse<Json>) {
     if (!this.#connected) {
       throw new Error(
         'It is not possible to reply after the port has disconnected',