diff --git a/extensions/bluebubbles/src/catchup.test.ts b/extensions/bluebubbles/src/catchup.test.ts
index 7e4a265dea7..4116fcbb513 100644
--- a/extensions/bluebubbles/src/catchup.test.ts
+++ b/extensions/bluebubbles/src/catchup.test.ts
@@ -115,16 +115,21 @@ describe("runBlueBubblesCatchup", () => {
 
     let fetchCount = 0;
     let processCount = 0;
-    let resolveFetch: (() => void) | null = null;
+    let releaseFetch: (() => void) | undefined;
+    let fetchStartedResolve: (() => void) | undefined;
+    const fetchStarted = new Promise<void>((resolve) => {
+      fetchStartedResolve = resolve;
+    });
 
     const call1 = runBlueBubblesCatchup(makeTarget(), {
       now: () => now,
       fetchMessages: async () => {
         fetchCount++;
+        fetchStartedResolve?.();
         // Block until we fire the second call, so we can verify it
         // coalesces rather than starting a new run.
         await new Promise<void>((resolve) => {
-          resolveFetch = resolve;
+          releaseFetch = resolve;
         });
         return {
           resolved: true,
@@ -136,8 +141,9 @@ describe("runBlueBubblesCatchup", () => {
       },
     });
 
-    // Wait a tick for call1 to enter fetchMessages, then fire call2.
-    await new Promise<void>((resolve) => setTimeout(resolve, 5));
+    // Wait for call1 to enter fetchMessages, then fire call2. A fixed
+    // sleep is load-sensitive and can leave call1 permanently blocked.
+    await fetchStarted;
     const call2 = runBlueBubblesCatchup(makeTarget(), {
       now: () => now,
       fetchMessages: async () => {
@@ -149,7 +155,7 @@ describe("runBlueBubblesCatchup", () => {
       },
     });
 
-    resolveFetch!();
+    releaseFetch?.();
     const [r1, r2] = await Promise.all([call1, call2]);
 
     expect(fetchCount).toBe(1); // second call coalesced, didn't re-fetch
diff --git a/test/vitest/vitest.extension-bluebubbles.config.ts b/test/vitest/vitest.extension-bluebubbles.config.ts
index 2816e4b5369..f9931ee732f 100644
--- a/test/vitest/vitest.extension-bluebubbles.config.ts
+++ b/test/vitest/vitest.extension-bluebubbles.config.ts
@@ -17,7 +17,6 @@ export function createExtensionBlueBubblesVitestConfig(
     {
       dir: "extensions",
       env,
-      isolate: true,
       name: "extension-bluebubbles",
       passWithNoTests: true,
       setupFiles: ["test/setup.extensions.ts"],