diff --git a/src/Stache/Indexes/Submissions/Site.php b/src/Stache/Indexes/Submissions/Site.php
new file mode 100644
index 00000000000..05b229f6824
--- /dev/null
+++ b/src/Stache/Indexes/Submissions/Site.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace Statamic\Stache\Indexes\Submissions;
+
+use Statamic\Stache\Indexes\Value;
+
+class Site extends Value
+{
+    public function getItemValue($item)
+    {
+        return $item->site()->handle();
+    }
+}
diff --git a/src/Stache/Stores/FormSubmissionsStore.php b/src/Stache/Stores/FormSubmissionsStore.php
index 4660f869168..8b617164b8b 100644
--- a/src/Stache/Stores/FormSubmissionsStore.php
+++ b/src/Stache/Stores/FormSubmissionsStore.php
@@ -7,6 +7,7 @@
 use Statamic\Facades\FormSubmission;
 use Statamic\Facades\Path;
 use Statamic\Facades\YAML;
+use Statamic\Stache\Indexes;
 use Statamic\Stache\Indexes\Value;
 use Statamic\Support\Str;
 use Statamic\Yaml\ParseException;
@@ -18,6 +19,7 @@ class FormSubmissionsStore extends ChildStore
     protected $storeIndexes = [
         'form',
         'date',
+        'site' => Indexes\Submissions\Site::class,
     ];
 
     public function getItemKey($item)
diff --git a/tests/Forms/SubmissionQueryBuilderTest.php b/tests/Forms/SubmissionQueryBuilderTest.php
index 1395fb0fabb..45c5095842e 100644
--- a/tests/Forms/SubmissionQueryBuilderTest.php
+++ b/tests/Forms/SubmissionQueryBuilderTest.php
@@ -7,6 +7,8 @@
 use Statamic\Contracts\Forms\Submission;
 use Statamic\Facades\Form;
 use Statamic\Facades\FormSubmission;
+use Statamic\Facades\Site;
+use Statamic\Facades\Stache;
 use Tests\PreventSavingStacheItemsToDisk;
 use Tests\TestCase;
 
@@ -506,6 +508,25 @@ public function it_filters_by_site()
 
         $this->assertEquals(['b', 'c'], $this->ids(FormSubmission::query()->where('site', 'fr')->get()));
         $this->assertEquals(['a'], $this->ids(FormSubmission::query()->where('site', 'en')->get()));
+        $this->assertEquals(['b', 'c'], $this->ids(FormSubmission::query()->where('site', Site::get('fr'))->get()));
+    }
+
+    #[Test]
+    public function it_stores_site_handles_in_the_site_index()
+    {
+        $this->setSites([
+            'en' => ['url' => '/'],
+            'fr' => ['url' => '/fr'],
+        ]);
+
+        $form = tap(Form::make('test'))->save();
+        $en = tap(FormSubmission::make()->form($form)->site('en'))->save();
+        $fr = tap(FormSubmission::make()->form($form)->site('fr'))->save();
+
+        $this->assertSame([
+            "test::{$en->id()}" => 'en',
+            "test::{$fr->id()}" => 'fr',
+        ], Stache::store('form-submissions')->store('test')->index('site')->items()->all());
     }
 
     #[Test]