diff --git a/packages/signals/tests/attribution.test.ts b/packages/signals/tests/attribution.test.ts
index 84d1a3735d..c3edb78859 100644
--- a/packages/signals/tests/attribution.test.ts
+++ b/packages/signals/tests/attribution.test.ts
@@ -503,9 +503,12 @@ describe("why-did-this-run attribution", () => {
       while (performance.now() < end);
     };
     const [n, setN] = createSignal(0, { name: "n" });
+    // 40 ms, not 10: self-times are wall-clock, and on a loaded CI runner a
+    // scheduling pause inside the cheap effect measured 17.9 ms against the
+    // memo's 10.1 ms. The ranking asserted below needs the gap to be wide.
     const slow = createMemo(
       () => {
-        spin(10);
+        spin(40);
         return n();
       },
       { name: "slow-memo" }
diff --git a/packages/signals/tests/treeshake.test.ts b/packages/signals/tests/treeshake.test.ts
index 9b7780b324..630bcefdd8 100644
--- a/packages/signals/tests/treeshake.test.ts
+++ b/packages/signals/tests/treeshake.test.ts
@@ -67,7 +67,10 @@ function retainedFrom(retained: string[], names: string[]): string[] {
   return names.filter(name => retained.some(id => id.includes(name)));
 }
 
-describe("pay-for-use tree-shaking (#2883)", () => {
+// Every test runs a full Vite build of a fixture, and the first one pays the
+// bundler's cold start: under the whole suite's load on CI it ran past
+// vitest's 5 s default (5,295 ms) while asserting nothing wrong.
+describe("pay-for-use tree-shaking (#2883)", { timeout: 30_000 }, () => {
   it("core floor sheds every optional feature module", async () => {
     const { minifiedBytes, retained } = await bundleFixture(
       `export { createSignal, createMemo, createEffect, createRoot, flush } from "sigsrc";`