diff --git a/swh/deposit/api/common.py b/swh/deposit/api/common.py
--- a/swh/deposit/api/common.py
+++ b/swh/deposit/api/common.py
@@ -836,6 +836,7 @@
                 .order_by("-id")[0:1]
                 .get()
             )
+            deposit.origin_url = origin_url
 
         if "atom:external_identifier" in metadata:
             # Deprecated tag.
@@ -846,12 +847,7 @@
                 raise DepositError(
                     BAD_REQUEST,
                     "<external_identifier> is deprecated, you should only use "
-                    "<swh:create_origin> from now on.",
-                )
-
-            if deposit.parent:
-                raise DepositError(
-                    BAD_REQUEST, "<external_identifier> is deprecated.",
+                    "<swh:create_origin> and <swh:add_to_origin> from now on.",
                 )
 
             if headers.slug and metadata["atom:external_identifier"] != headers.slug:
diff --git a/swh/deposit/tests/api/test_collection_add_to_origin.py b/swh/deposit/tests/api/test_collection_add_to_origin.py
--- a/swh/deposit/tests/api/test_collection_add_to_origin.py
+++ b/swh/deposit/tests/api/test_collection_add_to_origin.py
@@ -51,6 +51,7 @@
 
     assert new_deposit != deposit
     assert new_deposit.parent == deposit
+    assert new_deposit.origin_url == origin_url
 
 
 def test_add_deposit_add_to_origin_conflict(
@@ -133,7 +134,7 @@
     )
 
     assert response.status_code == status.HTTP_400_BAD_REQUEST
-    assert b"&lt;external_identifier&gt; is deprecated." in response.content
+    assert b"&lt;external_identifier&gt; is deprecated" in response.content
 
 
 def test_post_deposit_atom_403_add_to_wrong_origin_url_prefix(