diff --git a/backend/hitas/migrations/0017_alter_aparmentdocument_modified_at_and_more.py b/backend/hitas/migrations/0017_alter_aparmentdocument_modified_at_and_more.py
new file mode 100644
index 000000000..604687f9e
--- /dev/null
+++ b/backend/hitas/migrations/0017_alter_aparmentdocument_modified_at_and_more.py
@@ -0,0 +1,23 @@
+# Generated by Django 4.2.16 on 2025-01-24 11:29
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('hitas', '0016_external_report_view'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='aparmentdocument',
+            name='modified_at',
+            field=models.DateTimeField(auto_now_add=True),
+        ),
+        migrations.AlterField(
+            model_name='housingcompanydocument',
+            name='modified_at',
+            field=models.DateTimeField(auto_now_add=True),
+        ),
+    ]
diff --git a/backend/hitas/models/document.py b/backend/hitas/models/document.py
index df876392a..840e9e95a 100644
--- a/backend/hitas/models/document.py
+++ b/backend/hitas/models/document.py
@@ -33,7 +33,9 @@ class BaseDocument(ExternalSafeDeleteHitasModel):
     display_name = models.CharField(max_length=1024)
     original_filename = models.CharField(max_length=255)
     created_at = models.DateTimeField(auto_now_add=True)
-    modified_at = models.DateTimeField(auto_now=True)
+    # This field is using `auto_now_add=True` instead of `auto_now=True` because
+    # we want to set the `modified_at` using custom logic for example when the file is updated.
+    modified_at = models.DateTimeField(auto_now_add=True)
 
     class Meta:
         abstract = True
diff --git a/backend/hitas/tests/apis/test_api_document.py b/backend/hitas/tests/apis/test_api_document.py
index 7685a1e7f..d886cbad4 100644
--- a/backend/hitas/tests/apis/test_api_document.py
+++ b/backend/hitas/tests/apis/test_api_document.py
@@ -1,6 +1,9 @@
+from datetime import timedelta
+
 import pytest
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.urls import reverse
+from django.utils import timezone
 from rest_framework import status
 
 from hitas.models import (
@@ -176,6 +179,57 @@ def test__api__housingcompany__document__update__file(api_client: HitasAPIClient
     assert not document.file.storage.exists(old_filename), "Old file should be deleted from storage"
 
 
+@pytest.mark.django_db
+def test__api__document__modified_at(api_client: HitasAPIClient):
+    apartment = ApartmentFactory()
+    document = AparmentDocument.objects.create(
+        apartment=apartment, display_name="Test document", original_filename="testfile.txt"
+    )
+    response = api_client.put(
+        reverse(
+            "hitas:document-detail", args=[apartment.housing_company.uuid.hex, apartment.uuid.hex, document.uuid.hex]
+        ),
+        data={
+            "display_name": "Test document",
+            "file_content": SimpleUploadedFile("testfile.txt", b"test file content 1", content_type="text/plain"),
+        },
+    )
+    assert response.status_code == status.HTTP_200_OK
+    document.refresh_from_db()
+
+    # Pretend document was created 2 days ago
+    document.created_at = timezone.now() - timedelta(days=2)
+    document.modified_at = timezone.now() - timedelta(days=2)
+    document.save()
+    initial_modified_at = document.modified_at
+
+    # Update display_name
+    response = api_client.put(
+        reverse(
+            "hitas:document-detail", args=[apartment.housing_company.uuid.hex, apartment.uuid.hex, document.uuid.hex]
+        ),
+        data={
+            "display_name": "New name",
+        },
+    )
+    assert response.status_code == status.HTTP_200_OK
+    document.refresh_from_db()
+    assert document.modified_at == initial_modified_at, "modified_at should not change when updating display_name only"
+
+    response = api_client.put(
+        reverse(
+            "hitas:document-detail", args=[apartment.housing_company.uuid.hex, apartment.uuid.hex, document.uuid.hex]
+        ),
+        data={
+            "display_name": "New name",
+            "file_content": SimpleUploadedFile("testfile.txt", b"test file content 2", content_type="text/plain"),
+        },
+    )
+    assert response.status_code == status.HTTP_200_OK
+    document.refresh_from_db()
+    assert document.modified_at > initial_modified_at, "modified_at should change when updating file"
+
+
 @pytest.mark.django_db
 def test__api__apartment__document__redirect(api_client: HitasAPIClient):
     apartment = ApartmentFactory()
diff --git a/backend/hitas/views/document.py b/backend/hitas/views/document.py
index a754cba05..0f91c1bf1 100644
--- a/backend/hitas/views/document.py
+++ b/backend/hitas/views/document.py
@@ -1,4 +1,5 @@
 from django.shortcuts import redirect
+from django.utils import timezone
 from rest_framework import serializers
 from rest_framework.decorators import action
 from rest_framework.parsers import JSONParser, MultiPartParser
@@ -45,6 +46,7 @@ def update(self, instance, validated_data):
         file = validated_data.get("file")
         if file:
             validated_data["original_filename"] = file.name
+            validated_data["modified_at"] = timezone.now()
         return super().update(instance, validated_data)