diff --git a/alexandria/core/tests/__snapshots__/test_viewsets.ambr b/alexandria/core/tests/__snapshots__/test_viewsets.ambr
index 6b00be96..30dd98a9 100644
--- a/alexandria/core/tests/__snapshots__/test_viewsets.ambr
+++ b/alexandria/core/tests/__snapshots__/test_viewsets.ambr
@@ -2226,6 +2226,8 @@
       'SELECT "alexandria_core_mark"."created_at", "alexandria_core_mark"."created_by_user", "alexandria_core_mark"."created_by_group", "alexandria_core_mark"."modified_at", "alexandria_core_mark"."modified_by_user", "alexandria_core_mark"."modified_by_group", "alexandria_core_mark"."metainfo", "alexandria_core_mark"."slug", "alexandria_core_mark"."name", "alexandria_core_mark"."description" FROM "alexandria_core_mark" WHERE "alexandria_core_mark"."slug" = \'father-should-keep\' LIMIT 21',
       'SELECT "alexandria_core_tag"."created_at", "alexandria_core_tag"."created_by_user", "alexandria_core_tag"."created_by_group", "alexandria_core_tag"."modified_at", "alexandria_core_tag"."modified_by_user", "alexandria_core_tag"."modified_by_group", "alexandria_core_tag"."metainfo", "alexandria_core_tag"."id", "alexandria_core_tag"."name", "alexandria_core_tag"."description", "alexandria_core_tag"."tag_synonym_group_id" FROM "alexandria_core_tag" INNER JOIN "alexandria_core_document_tags" ON ("alexandria_core_tag"."id" = "alexandria_core_document_tags"."tag_id") WHERE ("alexandria_core_document_tags"."document_id" = \'9dd4e461268c8034f5c8564e155c67a6\'::uuid AND NOT ("alexandria_core_tag"."id" IN (SELECT U0."id" FROM "alexandria_core_tag" U0 INNER JOIN "alexandria_core_document_tags" U1 ON (U0."id" = U1."tag_id") WHERE U1."document_id" = \'9dd4e461268c8034f5c8564e155c67a6\'::uuid)))',
       'SELECT "alexandria_core_mark"."created_at", "alexandria_core_mark"."created_by_user", "alexandria_core_mark"."created_by_group", "alexandria_core_mark"."modified_at", "alexandria_core_mark"."modified_by_user", "alexandria_core_mark"."modified_by_group", "alexandria_core_mark"."metainfo", "alexandria_core_mark"."slug", "alexandria_core_mark"."name", "alexandria_core_mark"."description" FROM "alexandria_core_mark" INNER JOIN "alexandria_core_document_marks" ON ("alexandria_core_mark"."slug" = "alexandria_core_document_marks"."mark_id") WHERE ("alexandria_core_document_marks"."document_id" = \'9dd4e461268c8034f5c8564e155c67a6\'::uuid AND NOT ("alexandria_core_mark"."slug" IN (SELECT U0."slug" FROM "alexandria_core_mark" U0 INNER JOIN "alexandria_core_document_marks" U1 ON (U0."slug" = U1."mark_id") WHERE U1."document_id" = \'9dd4e461268c8034f5c8564e155c67a6\'::uuid)))',
+      'SELECT "alexandria_core_document"."created_at", "alexandria_core_document"."created_by_user", "alexandria_core_document"."created_by_group", "alexandria_core_document"."modified_at", "alexandria_core_document"."modified_by_user", "alexandria_core_document"."modified_by_group", "alexandria_core_document"."metainfo", "alexandria_core_document"."id", "alexandria_core_document"."title", "alexandria_core_document"."description", "alexandria_core_document"."category_id", "alexandria_core_document"."date" FROM "alexandria_core_document" WHERE "alexandria_core_document"."id" = \'9dd4e461268c8034f5c8564e155c67a6\'::uuid LIMIT 21',
+      'SELECT "alexandria_core_category"."created_at", "alexandria_core_category"."created_by_user", "alexandria_core_category"."created_by_group", "alexandria_core_category"."modified_at", "alexandria_core_category"."modified_by_user", "alexandria_core_category"."modified_by_group", "alexandria_core_category"."metainfo", "alexandria_core_category"."slug", "alexandria_core_category"."name", "alexandria_core_category"."description", "alexandria_core_category"."allowed_mime_types", "alexandria_core_category"."color", "alexandria_core_category"."parent_id" FROM "alexandria_core_category" WHERE "alexandria_core_category"."slug" = \'note-act-source\' LIMIT 21',
       '''
         UPDATE "alexandria_core_document" SET "created_at" = '2017-05-21 00:00:00+00:00'::timestamptz, "created_by_user" = 'admin', "created_by_group" = 'admin', "modified_at" = '2017-05-21 00:00:00+00:00'::timestamptz, "modified_by_user" = 'admin', "modified_by_group" = 'admin', "metainfo" = '{}'::jsonb, "title" = 'Michael Edwards', "description" = 'Open else look tree arm responsibility week. Environmental statement bag someone them style.
         Public these health team change. Tax final upon stay sing middle suggest.', "category_id" = 'note-act-source', "date" = '1999-11-26'::date WHERE "alexandria_core_document"."id" = '9dd4e461268c8034f5c8564e155c67a6'::uuid
@@ -2243,7 +2245,7 @@
       'BEGIN',
       'COMMIT',
     ]),
-    'query_count': 19,
+    'query_count': 21,
     'request': dict({
       'CONTENT_LENGTH': '813',
       'CONTENT_TYPE': 'application/vnd.api+json',
diff --git a/alexandria/core/tests/test_validation.py b/alexandria/core/tests/test_validation.py
index e6f4cd4f..677dfed9 100644
--- a/alexandria/core/tests/test_validation.py
+++ b/alexandria/core/tests/test_validation.py
@@ -4,14 +4,14 @@
 from generic_permissions.config import ValidatorsConfig
 from generic_permissions.validation import validator_for
 
-from alexandria.core.models import Document
+from alexandria.core.models import Tag
 
 
-def test_custom_validation(db, reset_config_classes, document, file, admin_client):
+def test_custom_validation(db, reset_config_classes, tag, file, admin_client):
     call_counter = Counter()
 
     class TestValidator:
-        @validator_for(Document)
+        @validator_for(Tag)
         def validate(self, data, context):
             data["created_by_group"] = "foobar"
             call_counter["validate"] += 1
@@ -21,17 +21,12 @@ def validate(self, data, context):
 
     ValidatorsConfig.register_handler_class(TestValidator)
 
-    url = reverse("document-detail", args=[document.pk])
+    url = reverse("tag-detail", args=[tag.pk])
 
     # first, ensure validator is called for Document
     admin_client.patch(url, json={})
     assert call_counter["validate"] == 1
 
     # See if the validation had some effect
-    document.refresh_from_db()
-    assert document.created_by_group == "foobar"
-
-    # second, ensure validator is not called for File
-    url = reverse("file-detail", args=[file.pk])
-    admin_client.patch(url, json={})
-    assert call_counter["validate"] == 1
+    tag.refresh_from_db()
+    assert tag.created_by_group == "foobar"
diff --git a/alexandria/core/tests/test_views.py b/alexandria/core/tests/test_views.py
index 8b7b8419..4df5de2f 100644
--- a/alexandria/core/tests/test_views.py
+++ b/alexandria/core/tests/test_views.py
@@ -368,6 +368,37 @@ def test_document_delete_some_tags(admin_client, tag_factory, document_factory):
     )
 
 
+def test_move_document_to_new_category(
+    admin_client, category_factory, file_factory, document_factory
+):
+    category_not_allowed = category_factory.create(allowed_mime_types=["plain/text"])
+    category_allowed = category_factory.create(allowed_mime_types=["image/jpeg"])
+    document = document_factory()
+    file_factory.create(document=document, name="Image.jpeg", mime_type="image/jpeg")
+
+    url = reverse("document-detail", args=[document.pk])
+
+    data = {
+        "data": {
+            "type": "documents",
+            "id": document.pk,
+            "relationships": {
+                "category": {
+                    "data": {"id": category_not_allowed.pk, "type": "categories"}
+                }
+            },
+        }
+    }
+
+    response = admin_client.patch(url, data)
+
+    assert response.status_code == HTTP_400_BAD_REQUEST
+
+    data["data"]["relationships"]["category"]["data"]["id"] = category_allowed.pk
+    response = admin_client.patch(url, data)
+    assert response.status_code == HTTP_200_OK
+
+
 @pytest.mark.parametrize(
     "presigned, expected_status",
     [(True, HTTP_200_OK), (False, HTTP_403_FORBIDDEN)],
diff --git a/alexandria/core/validations.py b/alexandria/core/validations.py
index 9af7f9e2..6d0b6960 100644
--- a/alexandria/core/validations.py
+++ b/alexandria/core/validations.py
@@ -8,7 +8,7 @@
 from generic_permissions.validation import validator_for
 from rest_framework.exceptions import ValidationError
 
-from alexandria.core.models import File
+from alexandria.core.models import Document, File
 
 log = logging.getLogger(__name__)
 
@@ -101,3 +101,15 @@ def validate_file(self, data, context):
         data["mime_type"] = content_type_header
 
         return data
+
+    @validator_for(Document)
+    def validate_document(self, data, context):
+        if context["request"].method == "PATCH" and "category" in data:
+            category = data["category"]
+            document = context["view"].get_object()
+            if not document.category.pk == category.pk:
+                # Validate if a document is moved to another category that the
+                # mime type of the file is still compatible with the category's
+                # mime types.
+                validate_mime_type(document.get_latest_original().mime_type, category)
+        return data