diff --git a/extensions/voice-call/src/media-stream.test.ts b/extensions/voice-call/src/media-stream.test.ts
index 18eaf5113c4..1a6a194a255 100644
--- a/extensions/voice-call/src/media-stream.test.ts
+++ b/extensions/voice-call/src/media-stream.test.ts
@@ -40,12 +40,15 @@ const createDeferred = (): {
   resolve: () => void;
   reject: (error: Error) => void;
 } => {
-  let resolve!: () => void;
-  let reject!: (error: Error) => void;
+  let resolve: (() => void) | undefined;
+  let reject: ((error: Error) => void) | undefined;
   const promise = new Promise<void>((resolvePromise, rejectPromise) => {
     resolve = resolvePromise;
     reject = rejectPromise;
   });
+  if (!resolve || !reject) {
+    throw new Error("Expected deferred callbacks to be initialized");
+  }
   return { promise, resolve, reject };
 };
 
@@ -80,10 +83,13 @@ describe("MediaStreamHandler TTS queue", () => {
     const started: number[] = [];
     const finished: number[] = [];
 
-    let resolveFirst!: () => void;
+    let resolveFirst: (() => void) | undefined;
     const firstGate = new Promise<void>((resolve) => {
       resolveFirst = resolve;
     });
+    if (!resolveFirst) {
+      throw new Error("Expected first TTS gate resolver to be initialized");
+    }
 
     const first = handler.queueTts("stream-1", async () => {
       started.push(1);
diff --git a/extensions/voice-call/src/webhook.test.ts b/extensions/voice-call/src/webhook.test.ts
index 83254d182fd..6792d366829 100644
--- a/extensions/voice-call/src/webhook.test.ts
+++ b/extensions/voice-call/src/webhook.test.ts
@@ -1081,14 +1081,19 @@ describe("VoiceCallWebhookServer pre-auth webhook guards", () => {
     const server = new VoiceCallWebhookServer(config, manager, twilioProvider);
 
     let enteredReads = 0;
-    let releaseReads!: () => void;
-    let unblockReadBodies!: () => void;
+    let releaseReads: (() => void) | undefined;
+    let unblockReadBodies: (() => void) | undefined;
     const enteredEightReads = new Promise<void>((resolve) => {
       releaseReads = resolve;
     });
     const unblockReads = new Promise<void>((resolve) => {
       unblockReadBodies = resolve;
     });
+    if (!releaseReads || !unblockReadBodies) {
+      throw new Error("Expected webhook read gates to be initialized");
+    }
+    const releaseEnteredReads = releaseReads;
+    const unblockStartedReads = unblockReadBodies;
     const readBodySpy = vi.spyOn(
       server as unknown as {
         readBody: (req: unknown, maxBytes: number, timeoutMs?: number) => Promise<string>;
@@ -1098,7 +1103,7 @@ describe("VoiceCallWebhookServer pre-auth webhook guards", () => {
     readBodySpy.mockImplementation(async () => {
       enteredReads += 1;
       if (enteredReads === 8) {
-        releaseReads();
+        releaseEnteredReads();
       }
       if (enteredReads <= 8) {
         await unblockReads;
@@ -1118,12 +1123,12 @@ describe("VoiceCallWebhookServer pre-auth webhook guards", () => {
       expect(rejected.status).toBe(429);
       expect(await rejected.text()).toBe("Too Many Requests");
 
-      unblockReadBodies();
+      unblockStartedReads();
 
       const settled = await Promise.all(inFlightRequests);
       expect(settled.map((response) => response.status)).toEqual(Array(8).fill(200));
     } finally {
-      unblockReadBodies();
+      unblockStartedReads();
       readBodySpy.mockRestore();
       await server.stop();
     }
@@ -1148,14 +1153,19 @@ describe("VoiceCallWebhookServer pre-auth webhook guards", () => {
     ).runWebhookPipeline.bind(server);
 
     let enteredReads = 0;
-    let releaseReads!: () => void;
-    let unblockReadBodies!: () => void;
+    let releaseReads: (() => void) | undefined;
+    let unblockReadBodies: (() => void) | undefined;
     const enteredEightReads = new Promise<void>((resolve) => {
       releaseReads = resolve;
     });
     const unblockReads = new Promise<void>((resolve) => {
       unblockReadBodies = resolve;
     });
+    if (!releaseReads || !unblockReadBodies) {
+      throw new Error("Expected webhook read gates to be initialized");
+    }
+    const releaseEnteredReads = releaseReads;
+    const unblockStartedReads = unblockReadBodies;
     const readBodySpy = vi.spyOn(
       server as unknown as {
         readBody: (req: unknown, maxBytes: number, timeoutMs?: number) => Promise<string>;
@@ -1165,7 +1175,7 @@ describe("VoiceCallWebhookServer pre-auth webhook guards", () => {
     readBodySpy.mockImplementation(async () => {
       enteredReads += 1;
       if (enteredReads === 8) {
-        releaseReads();
+        releaseEnteredReads();
       }
       await unblockReads;
       return "CallSid=CA123&SpeechResult=hello";
@@ -1193,12 +1203,12 @@ describe("VoiceCallWebhookServer pre-auth webhook guards", () => {
       expect(rejected.body).toBe("Too Many Requests");
       expect(readBodySpy).toHaveBeenCalledTimes(8);
 
-      unblockReadBodies();
+      unblockStartedReads();
 
       const settled = await Promise.all(inFlightRequests);
       expect(settled.map((response) => response.statusCode)).toEqual(Array(8).fill(200));
     } finally {
-      unblockReadBodies();
+      unblockStartedReads();
       readBodySpy.mockRestore();
     }
   });