diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index f1370f66a..3aae94e93 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -103,8 +103,8 @@ export class BlobReporter implements Reporter {
       outputFile = [
         'blob',
         this.ctx.config.mergeReportsLabel,
-        shard ? `-${shard.index}-${shard.count}` : '',
-      ].join('')
+        shard ? `${shard.index}-${shard.count}` : '',
+      ].filter(Boolean).join('-')
 
       outputFile = `${sanitizeFilePath(outputFile)}.json`
 
diff --git a/test/e2e/test/reporters/merge-reports.test.ts b/test/e2e/test/reporters/merge-reports.test.ts
index 18a6907c0..36a29856b 100644
--- a/test/e2e/test/reporters/merge-reports.test.ts
+++ b/test/e2e/test/reporters/merge-reports.test.ts
@@ -2,7 +2,7 @@ import type { RunVitestConfig } from '#test-utils'
 import type { File, Test } from '@vitest/runner/types'
 import type { TestUserConfig, Vitest } from 'vitest/node'
 import type { MergeReport } from 'vitest/src/node/reporters/blob.js'
-import { existsSync, rmSync } from 'node:fs'
+import { existsSync, readdirSync, rmSync } from 'node:fs'
 import { mkdir, writeFile } from 'node:fs/promises'
 import { buildTestTree, runVitest, useFS } from '#test-utils'
 import { playwright } from '@vitest/browser-playwright'
@@ -652,10 +652,17 @@ test("macos only", () => {})
       },
     }
   `)
+  const blobDir = resolve(root, '.vitest/blob')
   const result = await runVitest({
     root,
-    mergeReports: resolve(root, '.vitest/blob'),
+    mergeReports: blobDir,
   })
+  expect(readdirSync(blobDir)).toMatchInlineSnapshot(`
+    [
+      "blob-linux.json",
+      "blob-macos.json",
+    ]
+  `)
   expect(trimReporterOutput(result.stdout)).toMatchInlineSnapshot(`
     "✓  linux  first.test.ts > always good <time>
      ✓  linux  first.test.ts > works on linux <time>