diff --git a/src/documents/filters.py b/src/documents/filters.py
index 00a47552db..54cec180f6 100644
--- a/src/documents/filters.py
+++ b/src/documents/filters.py
@@ -15,7 +15,6 @@ import dateparser
 from django.conf import settings
 from django.contrib.contenttypes.models import ContentType
 from django.db.models import Case
-from django.db.models import CharField
 from django.db.models import Count
 from django.db.models import Exists
 from django.db.models import IntegerField
@@ -208,36 +207,30 @@ class EffectiveContentFilter(Filter):
 @extend_schema_field(serializers.BooleanField)
 class SharedByUser(Filter):
     def filter(self, qs, value):
+        if value is None:
+            return qs
+
         ctype = ContentType.objects.get_for_model(self.model)
         UserObjectPermission = get_user_obj_perms_model()
         GroupObjectPermission = get_group_obj_perms_model()
-        # see https://github.com/paperless-ngx/paperless-ngx/issues/5392, we limit subqueries
-        # to 1 because Postgres doesn't like returning > 1 row, but all we care about is > 0
-        return (
-            qs.filter(
-                owner_id=value,
-            )
-            .annotate(
-                num_shared_users=Count(
-                    UserObjectPermission.objects.filter(
-                        content_type=ctype,
-                        object_pk=Cast(OuterRef("pk"), CharField()),
-                    ).values("user_id")[:1],
-                ),
-            )
-            .annotate(
-                num_shared_groups=Count(
-                    GroupObjectPermission.objects.filter(
-                        content_type=ctype,
-                        object_pk=Cast(OuterRef("pk"), CharField()),
-                    ).values("group_id")[:1],
-                ),
-            )
-            .filter(
-                Q(num_shared_users__gt=0) | Q(num_shared_groups__gt=0),
-            )
-            if value is not None
-            else qs
+        # Guardian stores object_pk as a string. Each grant table is read once,
+        # as an uncorrelated set of integer keys, because probing it per
+        # document by string key has no usable index (none leads with
+        # object_pk) and MariaDB re-scans the table for every owned document.
+        # DISTINCT keeps Postgres hashing each set once: without it a large
+        # group grant table exceeds work_mem and is re-scanned for every row.
+        shared_with_users = (
+            UserObjectPermission.objects.filter(content_type=ctype)
+            .values(shared_pk=Cast("object_pk", IntegerField()))
+            .distinct()
+        )
+        shared_with_groups = (
+            GroupObjectPermission.objects.filter(content_type=ctype)
+            .values(shared_pk=Cast("object_pk", IntegerField()))
+            .distinct()
+        )
+        return qs.filter(owner_id=value).filter(
+            Q(pk__in=shared_with_users) | Q(pk__in=shared_with_groups),
         )
 
 
diff --git a/src/documents/tests/test_api_documents.py b/src/documents/tests/test_api_documents.py
index eeb1ab59a9..7ee2023162 100644
--- a/src/documents/tests/test_api_documents.py
+++ b/src/documents/tests/test_api_documents.py
@@ -1480,6 +1480,45 @@ class TestDocumentApi(DirectoriesMixin, ConsumeTaskMixin, APITestCase):
             [u1_doc1.id],
         )
 
+    def test_shared_by_filter_matches_user_and_group_grants_once(self) -> None:
+        """
+        GIVEN:
+            - Documents owned by a user: one shared with a user, one shared with
+              a group, one shared with several users and a group, one unshared
+            - A shared document owned by someone else
+        WHEN:
+            - Documents are filtered by shared_by__id for the owner
+        THEN:
+            - Only the owner's shared documents are returned, each exactly once
+        """
+        owner = UserFactory(username="owner")
+        other = UserFactory(username="other")
+        reader1 = UserFactory(username="reader1")
+        reader2 = UserFactory(username="reader2")
+        group = Group.objects.create(name="readers")
+        grant_all_global(owner)
+
+        shared_with_user = DocumentFactory.create(owner=owner)
+        shared_with_group = DocumentFactory.create(owner=owner)
+        shared_widely = DocumentFactory.create(owner=owner)
+        DocumentFactory.create(owner=owner)
+        others_shared = DocumentFactory.create(owner=other)
+        grant_object(reader1, shared_with_user, "view_document")
+        grant_object(group, shared_with_group, "view_document")
+        for target in (reader1, reader2, group):
+            grant_object(target, shared_widely, "view_document")
+        grant_object(reader1, others_shared, "view_document")
+
+        self.client.force_authenticate(owner)
+        response = self.client.get(f"/api/documents/?shared_by__id={owner.id}")
+
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.assertEqual(response.data["count"], 3)
+        self.assertCountEqual(
+            [result["id"] for result in response.data["results"]],
+            [shared_with_user.id, shared_with_group.id, shared_widely.id],
+        )
+
     def test_document_owned_and_group_shared_not_duplicated_when_filtering_by_tags(
         self,
     ) -> None: