diff --git a/src/acp/server.startup.test.ts b/src/acp/server.startup.test.ts
index e35b2cb3f8d..d1f8c38ef3d 100644
--- a/src/acp/server.startup.test.ts
+++ b/src/acp/server.startup.test.ts
@@ -165,6 +165,18 @@ describe("serveAcpGateway startup", () => {
     return gateway;
   }
 
+  function getGatewayBootstrapParams(): { env?: unknown; gatewayUrl?: unknown } {
+    const firstCall = mockState.resolveGatewayClientBootstrap.mock.calls.at(0);
+    if (!firstCall) {
+      throw new Error("Expected gateway bootstrap resolution call");
+    }
+    const params = firstCall.at(0);
+    if (!params || typeof params !== "object") {
+      throw new Error("Expected gateway bootstrap params");
+    }
+    return params;
+  }
+
   function captureProcessSignalHandlers() {
     const signalHandlers = new Map<NodeJS.Signals, () => void>();
     const onceSpy = vi.spyOn(process, "once").mockImplementation(((
@@ -307,10 +319,8 @@ describe("serveAcpGateway startup", () => {
       const servePromise = serveAcpGateway({});
       await Promise.resolve();
 
-      const bootstrapParams = mockState.resolveGatewayClientBootstrap.mock.calls[0]?.[0] as
-        | { env?: unknown }
-        | undefined;
-      expect(bootstrapParams?.env).toBe(process.env);
+      const bootstrapParams = getGatewayBootstrapParams();
+      expect(bootstrapParams.env).toBe(process.env);
       expect(mockState.gatewayAuth[0]).toEqual({
         token: undefined,
         password: "resolved-secret-password", // pragma: allowlist secret
@@ -332,11 +342,9 @@ describe("serveAcpGateway startup", () => {
       });
       await Promise.resolve();
 
-      const bootstrapParams = mockState.resolveGatewayClientBootstrap.mock.calls[0]?.[0] as
-        | { env?: unknown; gatewayUrl?: unknown }
-        | undefined;
-      expect(bootstrapParams?.env).toBe(process.env);
-      expect(bootstrapParams?.gatewayUrl).toBe("wss://override.example/ws");
+      const bootstrapParams = getGatewayBootstrapParams();
+      expect(bootstrapParams.env).toBe(process.env);
+      expect(bootstrapParams.gatewayUrl).toBe("wss://override.example/ws");
 
       await emitHelloAndWaitForAgentSideConnection();
       await stopServeWithSigint(signalHandlers, servePromise);