diff --git a/apps/desktop/src/lib/markdown-blocks.test.ts b/apps/desktop/src/lib/markdown-blocks.test.ts
index 7b55cb035184..ff8d9495c6d4 100644
--- a/apps/desktop/src/lib/markdown-blocks.test.ts
+++ b/apps/desktop/src/lib/markdown-blocks.test.ts
@@ -130,6 +130,10 @@ describe('parseMarkdownIntoBlocksCached', () => {
     expect(parseMarkdownIntoBlocksCached(grown)).toEqual(parseMarkdownIntoBlocks(grown))
   })
 
+  // 12 seeds × 500 growing prefixes is ~6000 full+cached lexes; it first trips
+  // the pre-fix boundary at seed 11 / step 257, so the workload can't shrink
+  // without gutting the guard. The work is bounded but exceeds one test's 5s
+  // default budget, so raise the timeout rather than weaken the coverage.
   it('matches a full lex at every char-level streaming cut over noisy markdown (property fuzz)', () => {
     // Character-level append fuzz over the markdown control alphabet — the
     // harness that surfaced the setext-underline merge above. Growing a single
@@ -156,5 +160,5 @@ describe('parseMarkdownIntoBlocksCached', () => {
         expect(parseMarkdownIntoBlocksCached(text)).toEqual(parseMarkdownIntoBlocks(text))
       }
     }
-  })
+  }, 30_000)
 })