diff --git a/river/core/classworkflowobject.py b/river/core/classworkflowobject.py
index 8adbf53..39f6b3a 100644
--- a/river/core/classworkflowobject.py
+++ b/river/core/classworkflowobject.py
@@ -1,6 +1,6 @@
 from django.contrib import auth
 from django.contrib.contenttypes.models import ContentType
-from django.db.models import F, Q, IntegerField, Min
+from django.db.models import F, Q, Min, CharField
 from django.db.models.functions import Cast
 from django_cte import With
 
@@ -47,12 +47,12 @@ def get_available_approvals(self, as_user):
         ).with_cte(
             those_with_max_priority
         ).annotate(
-            object_id_as_int=Cast('object_id', IntegerField()),
+            object_id_as_str=Cast('object_id', CharField(max_length=200)),
             min_priority=those_with_max_priority.col.min_priority
         ).filter(min_priority=F("priority"))
 
         return workflow_objects.join(
-            approvals_with_max_priority, object_id_as_int=workflow_objects.col.pk
+            approvals_with_max_priority, object_id_as_str=workflow_objects.col.pk
         ).with_cte(
             workflow_objects
         ).filter(transition__source_state=getattr(workflow_objects.col, self.field_name + "_id"))
diff --git a/river/tests/core/test__instance_api.py b/river/tests/core/test__instance_api.py
index 1cd7687..0030346 100644
--- a/river/tests/core/test__instance_api.py
+++ b/river/tests/core/test__instance_api.py
@@ -3,9 +3,10 @@
 from hamcrest import assert_that, equal_to, has_item, has_property, raises, calling, has_length, is_not, all_of, none, has_items
 
 from river.models import TransitionApproval, PENDING, CANCELLED, APPROVED, Transition, JUMPED
-from river.models.factories import UserObjectFactory, StateObjectFactory, TransitionApprovalMetaFactory, PermissionObjectFactory, WorkflowFactory, TransitionMetaFactory
+from river.models.factories import UserObjectFactory, StateObjectFactory, TransitionApprovalMetaFactory, PermissionObjectFactory, WorkflowFactory, \
+    TransitionMetaFactory
 from river.tests.matchers import has_permission, has_transition
-from river.tests.models import BasicTestModel, ModelWithTwoStateFields
+from river.tests.models import BasicTestModel, ModelWithTwoStateFields, ModelWithStringPrimaryKey
 from river.tests.models.factories import BasicTestModelObjectFactory, ModelWithTwoStateFieldsObjectFactory
 from river.utils.exceptions import RiverException
 
@@ -1766,3 +1767,30 @@ def test_shouldJumpToASpecificStateWhenThereAreMultipleNextState(self):
                 )
             )
         )
+
+    def test_shouldNotCrashWhenAModelObjectWithStringPrimaryKeyIsApproved(self):
+        state1 = StateObjectFactory(label="state1")
+        state2 = StateObjectFactory(label="state2")
+
+        content_type = ContentType.objects.get_for_model(ModelWithStringPrimaryKey)
+        authorized_permission = PermissionObjectFactory(content_type=content_type)
+        authorized_user = UserObjectFactory(user_permissions=[authorized_permission])
+        workflow = WorkflowFactory(initial_state=state1, content_type=content_type, field_name="status")
+
+        transition_meta = TransitionMetaFactory.create(
+            workflow=workflow,
+            source_state=state1,
+            destination_state=state2,
+        )
+        TransitionApprovalMetaFactory.create(
+            workflow=workflow,
+            transition_meta=transition_meta,
+            priority=0,
+            permissions=[authorized_permission]
+        )
+
+        workflow_object = ModelWithStringPrimaryKey.objects.create()
+
+        assert_that(workflow_object.status, equal_to(state1))
+        workflow_object.river.status.approve(as_user=authorized_user)
+        assert_that(workflow_object.status, equal_to(state2))
diff --git a/river/tests/models/__init__.py b/river/tests/models/__init__.py
index dc7b1fa..9003c6e 100644
--- a/river/tests/models/__init__.py
+++ b/river/tests/models/__init__.py
@@ -1,3 +1,5 @@
+from uuid import uuid4
+
 from django.db import models
 
 from river.models.fields.state import StateField
@@ -28,3 +30,8 @@ class ModelForSlowCase2(models.Model):
 class ModelWithTwoStateFields(models.Model):
     status1 = StateField()
     status2 = StateField()
+
+
+class ModelWithStringPrimaryKey(models.Model):
+    custom_pk = models.CharField(max_length=200, primary_key=True, default=uuid4())
+    status = StateField()