diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0e72850..a2d01ad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ and this project adheres to
 ### Fixed
 
 - 🩹(mailbox) fix status of current mailboxes
+- 🚑️(backend) fix claim contains non-user field #548
 
 ## [1.6.0] - 2024-11-20
 
diff --git a/src/backend/core/authentication/backends.py b/src/backend/core/authentication/backends.py
index d51decb..d9f2102 100644
--- a/src/backend/core/authentication/backends.py
+++ b/src/backend/core/authentication/backends.py
@@ -220,13 +220,11 @@ class OIDCAuthenticationBackend(MozillaOIDCAuthenticationBackend):
 
     def update_user_if_needed(self, user, claims):
         """Update user claims if they have changed."""
-        has_changed = any(
-            value and value != getattr(user, key)
-            for key, value in claims.items()
-            if key != "sub"
-        )
-        if has_changed:
-            updated_claims = {
-                key: value for key, value in claims.items() if value and key != "sub"
-            }
+        updated_claims = {}
+        for key in ["email", "name"]:
+            claim_value = claims.get(key)
+            if claim_value and claim_value != getattr(user, key):
+                updated_claims[key] = claim_value
+
+        if updated_claims:
             self.UserModel.objects.filter(sub=user.sub).update(**updated_claims)
diff --git a/src/backend/core/tests/authentication/test_backends.py b/src/backend/core/tests/authentication/test_backends.py
index 522be7a..70e79c1 100644
--- a/src/backend/core/tests/authentication/test_backends.py
+++ b/src/backend/core/tests/authentication/test_backends.py
@@ -106,6 +106,39 @@ def test_authentication_getter_existing_user_change_fields(
     assert user.name == f"{first_name:s} {last_name:s}"
 
 
+def test_authentication_getter_existing_user_keep_fields(
+    django_assert_num_queries, monkeypatch
+):
+    """
+    Falsy values in claim should not update the user's fields.
+    """
+    klass = OIDCAuthenticationBackend()
+    user = factories.UserFactory(
+        name="John Doe", email="john.doe@example.com", with_organization=True
+    )
+
+    def get_userinfo_mocked(*args):
+        return {
+            "sub": user.sub,
+            "email": None,
+            "first_name": "",
+            "last_name": "",
+        }
+
+    monkeypatch.setattr(OIDCAuthenticationBackend, "get_userinfo", get_userinfo_mocked)
+
+    # No field changed no more query
+    with django_assert_num_queries(1):
+        authenticated_user = klass.get_or_create_user(
+            access_token="test-token", id_token=None, payload=None
+        )
+
+    assert user == authenticated_user
+    user.refresh_from_db()
+    assert user.email == "john.doe@example.com"
+    assert user.name == "John Doe"
+
+
 def test_authentication_getter_existing_user_via_email(
     django_assert_num_queries, monkeypatch
 ):
@@ -381,3 +414,42 @@ def test_authentication_getter_existing_user_via_email_update_organization(
     assert user == db_user
     assert user.organization is not None
     assert user.organization.domain_list == ["my-domain.com"]
+
+
+def test_authentication_getter_existing_user_with_registration_id(
+    monkeypatch,
+    settings,
+):
+    """
+    Authenticate a user who already exists with an organization registration ID.
+
+    This asserts the "update_user_if_needed" does not fail when the claim
+    contains the organization registration ID (or any value not present in the
+    User model).
+    """
+    settings.OIDC_ORGANIZATION_REGISTRATION_ID_FIELD = "registration_number"
+
+    klass = OIDCAuthenticationBackend()
+    _existing_user = factories.UserFactory(
+        sub="123",
+        name="John Doe",
+        email="people@example.com",
+    )
+
+    def get_userinfo_mocked(*args):
+        return {
+            "sub": "123",
+            "email": "people@example.com",
+            "first_name": "John",
+            "last_name": "Doe",
+            "registration_number": "12345678901234",
+        }
+
+    monkeypatch.setattr(OIDCAuthenticationBackend, "get_userinfo", get_userinfo_mocked)
+
+    user = klass.get_or_create_user(
+        access_token="test-token", id_token=None, payload=None
+    )
+
+    assert user.organization is not None
+    assert user.organization.registration_id_list == ["12345678901234"]