diff --git a/setra_client/models.py b/setra_client/models.py
index f1d62c19d80ad38ec611231c0e8f85f85fad8ae9..fc384e4c1fe989b85773a37f5ba9c096c6aac0fe 100644
--- a/setra_client/models.py
+++ b/setra_client/models.py
@@ -234,7 +234,7 @@ class Detail(BaseModel):
     anlegg: Optional[str]
     aktivitet: Optional[str]
     line_no: int
-    product_specification: int
+    product_specification: Optional[int]
     price: Optional[float]
     quantity: Optional[float]
 
diff --git a/tests/fixtures/detail_list_fixture.json b/tests/fixtures/detail_list_fixture.json
index 5116b0dd3d076cef1615544a891a93acca7d1060..61ec9bd87c6adc420bd210311c674e999d40ac3a 100644
--- a/tests/fixtures/detail_list_fixture.json
+++ b/tests/fixtures/detail_list_fixture.json
@@ -33,7 +33,7 @@
     "anlegg": "anlegg",
     "aktivitet": "aktivitet",
     "line_no": 1,
-    "product_specification": 213,
+    "product_specification": null,
     "price": "1234.00",
     "quantity": 2.0
   }
diff --git a/tests/fixtures/order_with_detail_fixture.json b/tests/fixtures/order_with_detail_fixture.json
index 474ee1127677eb49b585f7978b20cf1d721c34f5..3a420b57e716a432daec71303a970277b524d662 100644
--- a/tests/fixtures/order_with_detail_fixture.json
+++ b/tests/fixtures/order_with_detail_fixture.json
@@ -32,7 +32,7 @@
             "anlegg": "anlegg",
             "aktivitet": "aktivitet",
             "line_no": 1,
-            "product_specification": 213,
+            "product_specification": null,
             "price": 1234.0,
             "quantity": 2.0
         },