diff --git a/packages/compiler/src/frontend/lowering/lower-timers.ts b/packages/compiler/src/frontend/lowering/lower-timers.ts
index 445b49d3ae..23514c1dc9 100644
--- a/packages/compiler/src/frontend/lowering/lower-timers.ts
+++ b/packages/compiler/src/frontend/lowering/lower-timers.ts
@@ -341,14 +341,18 @@ function isRealTimerCallee(lowerer: Lowerer, callee: ts.Expression): boolean {
 }
 
 /** Marks a lowered timer call `realTimer` when its callee is a binding
- * mock.timers does not replace. */
+ * mock.timers does not replace. A call whose delay is stored first returns a
+ * `seqExpr` around the call, so the mark goes on the call inside it. */
 function markRealTimerCall(
   lowerer: Lowerer,
   expr: ts.CallExpression,
   lowered: IrExpr | null,
 ): IrExpr | null {
-  if (lowered?.kind !== "libCall" || !MOCKABLE_TIMER_FNS.has(lowered.fn)) return lowered;
-  return isRealTimerCallee(lowerer, expr.expression) ? { ...lowered, realTimer: true } : lowered;
+  const call = lowered?.kind === "seqExpr" ? lowered.result : lowered;
+  if (call?.kind !== "libCall" || !MOCKABLE_TIMER_FNS.has(call.fn)) return lowered;
+  if (!isRealTimerCallee(lowerer, expr.expression)) return lowered;
+  const marked: IrExpr = { ...call, realTimer: true };
+  return lowered?.kind === "seqExpr" ? { ...lowered, result: marked } : marked;
 }
 
 /** One timer call by MEMBER NAME — the shared lowering behind the ambient
diff --git a/packages/compiler/test/timer-delay-lowering.test.ts b/packages/compiler/test/timer-delay-lowering.test.ts
index deff90e25d..08b76b2eb4 100644
--- a/packages/compiler/test/timer-delay-lowering.test.ts
+++ b/packages/compiler/test/timer-delay-lowering.test.ts
@@ -5,8 +5,10 @@ import { expect, test } from "vitest";
 import { compile, deserializeModule } from "../src/index.js";
 import type { IrExpr } from "../src/ir/ir.js";
 
-/** The delay argument of every setTimeout/setInterval libCall in the module. */
-async function timerDelays(source: string): Promise<IrExpr[]> {
+type TimerCall = Extract<IrExpr, { kind: "libCall" }>;
+
+/** Every setTimeout/setInterval libCall in the module. */
+async function timerCalls(source: string): Promise<TimerCall[]> {
   const dir = await mkdtemp(join(tmpdir(), "scriptc-timer-delays-"));
   try {
     const entry = join(dir, "main.ts");
@@ -16,7 +18,7 @@ async function timerDelays(source: string): Promise<IrExpr[]> {
     if (!result.ok)
       throw new Error(result.diagnostics.map((d) => `${d.code}: ${d.message}`).join("\n"));
     const mod = deserializeModule(await readFile(outPath, "utf8"));
-    const delays: IrExpr[] = [];
+    const calls: TimerCall[] = [];
     const visit = (value: unknown): void => {
       if (Array.isArray(value)) {
         for (const item of value) visit(item);
@@ -29,16 +31,21 @@ async function timerDelays(source: string): Promise<IrExpr[]> {
         typeof node.fn === "string" &&
         /^timers\.set(Timeout|TimeoutHandle|Interval)$/.test(node.fn)
       )
-        delays.push(node.args![1]!);
+        calls.push(node as TimerCall);
       for (const child of Object.values(value)) visit(child);
     };
     visit(mod.functions);
-    return delays;
+    return calls;
   } finally {
     await rm(dir, { recursive: true, force: true });
   }
 }
 
+/** The delay argument of every setTimeout/setInterval libCall in the module. */
+async function timerDelays(source: string): Promise<IrExpr[]> {
+  return (await timerCalls(source)).map((call) => call.args[1]!);
+}
+
 test("number delays pass to the timer unchanged", async () => {
   const delays = await timerDelays(
     `function arm(ms: number): void {
@@ -94,3 +101,23 @@ test("a number | undefined delay converts with ToNumber", async () => {
     });
   }
 });
+
+test("an imported timer call stays real through an untyped delay", async () => {
+  const calls = await timerCalls(
+    `import { setTimeout as realSetTimeout, setInterval as realSetInterval } from "node:timers";
+    function arm(delay: any): void {
+      realSetTimeout(() => console.log("a"), delay);
+      realSetInterval(() => console.log("b"), delay);
+      setTimeout(() => console.log("c"), delay);
+    }
+    arm(1);
+    export {};
+    `,
+  );
+  // An untyped delay waits in a hidden local, so the call sits inside a
+  // seqExpr; the callee still decides whether mock.timers routes it.
+  expect(calls.map((call) => call.realTimer)).toEqual([true, true, undefined]);
+  expect(calls[0]).toMatchObject({ fn: "timers.setTimeout" });
+  expect(calls[1]).toMatchObject({ fn: "timers.setInterval" });
+  expect(calls[2]).toMatchObject({ fn: "timers.setTimeout" });
+});
diff --git a/tests/corpus/timers-delay-warnings-mocked.ts b/tests/corpus/timers-delay-warnings-mocked.ts
index 75aba9b201..b7c610b3d2 100644
--- a/tests/corpus/timers-delay-warnings-mocked.ts
+++ b/tests/corpus/timers-delay-warnings-mocked.ts
@@ -2,7 +2,8 @@
 // While mock.timers mocks setTimeout and setInterval, the mocked functions
 // build no Timeout, so a negative or overflowing delay warns nothing;
 // after reset the real functions warn again, and a node:timers import is
-// never mocked.
+// never mocked: it schedules a real timer, including through an untyped
+// delay, whose conversion runs before the call.
 import { mock } from "node:test";
 import { setTimeout as realSetTimeout } from "node:timers";
 
@@ -15,7 +16,13 @@ const interval = setInterval(() => {
   clearInterval(interval);
 }, 2 ** 31);
 realSetTimeout(() => console.log("imported overflow"), 2 ** 32);
+function scheduleImported(delay: any): void {
+  realSetTimeout(() => console.log("imported untyped delay"), delay);
+}
+scheduleImported(1);
+setTimeout(() => console.log("mocked delay"), 1);
 mock.timers.tick(1);
+console.log("after tick");
 mock.timers.reset();
 
 setTimeout(() => console.log("real negative"), -5);