diff --git a/src/documents/filters.py b/src/documents/filters.py
index 0f49c7c27..c63484ee2 100644
--- a/src/documents/filters.py
+++ b/src/documents/filters.py
@@ -1,7 +1,9 @@
 from django.contrib.contenttypes.models import ContentType
+from django.db.models import CharField
 from django.db.models import Count
 from django.db.models import OuterRef
 from django.db.models import Q
+from django.db.models.functions import Cast
 from django_filters.rest_framework import BooleanFilter
 from django_filters.rest_framework import Filter
 from django_filters.rest_framework import FilterSet
@@ -119,7 +121,7 @@ class SharedByUser(Filter):
                 num_shared_users=Count(
                     UserObjectPermission.objects.filter(
                         content_type=ctype,
-                        object_pk=OuterRef("pk"),
+                        object_pk=Cast(OuterRef("pk"), CharField()),
                     ).values("user_id"),
                 ),
             )
@@ -127,7 +129,7 @@ class SharedByUser(Filter):
                 num_shared_groups=Count(
                     GroupObjectPermission.objects.filter(
                         content_type=ctype,
-                        object_pk=OuterRef("pk"),
+                        object_pk=Cast(OuterRef("pk"), CharField()),
                     ).values("group_id"),
                 ),
             )