diff --git a/superset-frontend/packages/superset-ui-switchboard/src/switchboard.test.ts b/superset-frontend/packages/superset-ui-switchboard/src/switchboard.test.ts
index 5bfe77903ff..352c508b2e8 100644
--- a/superset-frontend/packages/superset-ui-switchboard/src/switchboard.test.ts
+++ b/superset-frontend/packages/superset-ui-switchboard/src/switchboard.test.ts
@@ -95,8 +95,11 @@ class FakeMessageChannel {
     const port2 = new FakeMessagePort();
     port1.otherPort = port2;
     port2.otherPort = port1;
-    this.port1 = port1;
-    this.port2 = port2;
+    // FakeMessagePort only implements the subset of MessagePort that
+    // Switchboard exercises; cast at the boundary so the fake satisfies
+    // the consumer signature without weakening the production type.
+    this.port1 = port1 as unknown as MessagePort;
+    this.port2 = port2 as unknown as MessagePort;
   }
 }
 
diff --git a/superset-frontend/packages/superset-ui-switchboard/src/switchboard.ts b/superset-frontend/packages/superset-ui-switchboard/src/switchboard.ts
index d1df6136a50..46af6fb4d3e 100644
--- a/superset-frontend/packages/superset-ui-switchboard/src/switchboard.ts
+++ b/superset-frontend/packages/superset-ui-switchboard/src/switchboard.ts
@@ -88,7 +88,7 @@ function isError(message: Message): message is ErrorMessage {
  * Calling methods on the switchboard causes messages to be sent through the channel.
  */
 export class Switchboard {
-  port: MessagePort;
+  port!: MessagePort;
 
   name = '';
 
@@ -97,9 +97,9 @@ export class Switchboard {
   // used to make unique ids
   incrementor = 1;
 
-  debugMode: boolean;
+  debugMode = false;
 
-  private isInitialised: boolean;
+  private isInitialised = false;
 
   constructor(params?: Params) {
     if (!params) {