diff --git a/src/commands/gateway-install-token.test.ts b/src/commands/gateway-install-token.test.ts
index 2c2750c1632..55a84dc81c8 100644
--- a/src/commands/gateway-install-token.test.ts
+++ b/src/commands/gateway-install-token.test.ts
@@ -59,6 +59,14 @@ vi.mock("./random-token.js", () => ({
   randomToken: randomTokenMock,
 }));
 
+function firstReplaceConfigRequest(): unknown {
+  const [call] = replaceConfigFileMock.mock.calls;
+  if (!call) {
+    throw new Error("expected config replace call");
+  }
+  return call[0];
+}
+
 describe("resolveGatewayInstallToken", () => {
   beforeEach(() => {
     vi.clearAllMocks();
@@ -193,7 +201,7 @@ describe("resolveGatewayInstallToken", () => {
 
     expect(result.warnings.join("\n")).toContain("saving to config");
     expect(replaceConfigFileMock).toHaveBeenCalledOnce();
-    expect(replaceConfigFileMock.mock.calls[0]?.[0]).toStrictEqual({
+    expect(firstReplaceConfigRequest()).toStrictEqual({
       nextConfig: {
         gateway: {
           auth: {
diff --git a/src/commands/tasks-json.test.ts b/src/commands/tasks-json.test.ts
index ff023e0c41d..9f7aff500c7 100644
--- a/src/commands/tasks-json.test.ts
+++ b/src/commands/tasks-json.test.ts
@@ -21,7 +21,11 @@ function createRuntime(): RuntimeEnv {
 }
 
 function readJsonLog(runtime: RuntimeEnv): unknown {
-  return JSON.parse(String(vi.mocked(runtime.log).mock.calls[0]?.[0]));
+  const [call] = vi.mocked(runtime.log).mock.calls;
+  if (!call) {
+    throw new Error("expected runtime log call");
+  }
+  return JSON.parse(String(call[0]));
 }
 
 async function withTaskJsonStateDir(run: () => Promise<void>): Promise<void> {
diff --git a/src/daemon/systemd.test.ts b/src/daemon/systemd.test.ts
index 1f01a7c4406..aa208f28a83 100644
--- a/src/daemon/systemd.test.ts
+++ b/src/daemon/systemd.test.ts
@@ -62,7 +62,11 @@ const createWritableStreamMock = () => {
 };
 
 function requireFirstWrite(write: ReturnType<typeof vi.fn>): string {
-  const value = write.mock.calls[0]?.[0];
+  const [call] = write.mock.calls;
+  if (!call) {
+    throw new Error("expected systemd status write");
+  }
+  const [value] = call;
   if (value === undefined) {
     throw new Error("expected systemd status write");
   }
diff --git a/src/hooks/fire-and-forget.test.ts b/src/hooks/fire-and-forget.test.ts
index a061f0a906a..205d464d5f8 100644
--- a/src/hooks/fire-and-forget.test.ts
+++ b/src/hooks/fire-and-forget.test.ts
@@ -2,7 +2,11 @@ import { describe, expect, it, vi } from "vitest";
 import { fireAndForgetBoundedHook, fireAndForgetHook } from "./fire-and-forget.js";
 
 function requireFirstLog(logger: ReturnType<typeof vi.fn>): string {
-  const message = logger.mock.calls[0]?.[0];
+  const [call] = logger.mock.calls;
+  if (!call) {
+    throw new Error("expected log call");
+  }
+  const [message] = call;
   if (typeof message !== "string") {
     throw new Error("expected string log message");
   }