diff --git a/scripts/coverage-shards.spec.ts b/scripts/coverage-shards.spec.ts
index 8db6ac1aba..678011618e 100644
--- a/scripts/coverage-shards.spec.ts
+++ b/scripts/coverage-shards.spec.ts
@@ -28,11 +28,14 @@ describe('coverage shards', () => {
   it.each(coverageShards)('selects tests and source includes for $name', (shard) => {
     const args = coverageArgs(shard.name)
     for (const packageRoot of shard.packageRoots) {
-      expect(args).toContain(`packages/${packageRoot}`)
+      expect(args).toContain(`packages/${packageRoot}/`)
       expect(args).toContain(packageRoot.includes('/')
         ? `--coverage.include=packages/${packageRoot}/src/**/*.ts`
         : `--coverage.include=packages/${packageRoot}/*/src/**/*.ts`)
     }
+    if ('extraTestRoots' in shard) {
+      for (const testRoot of shard.extraTestRoots) expect(args).toContain(`${testRoot}/`)
+    }
     expect(args).toContain('scripts/test-invariants.spec.ts')
     expect(new Set(args).size).toBe(args.length)
   })
diff --git a/scripts/coverage-shards.ts b/scripts/coverage-shards.ts
index c58665f02a..84f4d1a63e 100644
--- a/scripts/coverage-shards.ts
+++ b/scripts/coverage-shards.ts
@@ -98,9 +98,11 @@ export function coverageArgs(name: string): string[] {
     throw new Error(`run-gates: unknown DSH_COVERAGE_SHARD ${JSON.stringify(name)}.`)
   }
 
+  // Vitest positional filters are substrings; the trailing separator keeps
+  // prefix-named sibling packages out of each lane.
   const testRoots = new Set([
-    ...shard.packageRoots.map(packageRoot => `packages/${packageRoot}`),
-    ...('extraTestRoots' in shard ? shard.extraTestRoots : []),
+    ...shard.packageRoots.map(packageRoot => `packages/${packageRoot}/`),
+    ...('extraTestRoots' in shard ? shard.extraTestRoots.map(testRoot => `${testRoot}/`) : []),
     'scripts/test-invariants.spec.ts',
   ])
   return [