diff --git a/apps/api/plane/authentication/adapter/base.py b/apps/api/plane/authentication/adapter/base.py
index 3a616a21c38..420407704e9 100644
--- a/apps/api/plane/authentication/adapter/base.py
+++ b/apps/api/plane/authentication/adapter/base.py
@@ -237,7 +237,7 @@ def save_user_data(self, user):
         user.last_active = timezone.now()
         user.last_login_time = timezone.now()
         user.last_login_ip = get_client_ip(request=self.request)
-        user.last_login_uagent = self.request.META.get("HTTP_USER_AGENT")
+        user.last_login_uagent = self.request.META.get("HTTP_USER_AGENT", "")
         user.token_updated_at = timezone.now()
         # Activate provisioned accounts that have never been deactivated.
         # Explicitly-deactivated accounts are rejected earlier in
diff --git a/apps/api/plane/tests/contract/app/test_authentication.py b/apps/api/plane/tests/contract/app/test_authentication.py
index 7a7d9640b74..4c2c44bd8b3 100644
--- a/apps/api/plane/tests/contract/app/test_authentication.py
+++ b/apps/api/plane/tests/contract/app/test_authentication.py
@@ -216,6 +216,31 @@ def test_user_login(self, django_client, setup_user, setup_instance):
         # The user should be authenticated regardless of the final page
         assert "_auth_user_id" in django_client.session
 
+    @pytest.mark.django_db
+    def test_user_login_without_user_agent_header(self, setup_user, setup_instance):
+        """Sign-in must succeed even when the request has no User-Agent header.
+
+        Regression test for #9672: some programmatic clients (e.g. Rust's
+        reqwest) send no User-Agent by default. `save_user_data()` used to
+        read `HTTP_USER_AGENT` with no default, so a missing header stored
+        `None` into the non-nullable `last_login_uagent` column and the
+        resulting `IntegrityError` bubbled up as an unhandled 500 instead of
+        completing the sign-in.
+        """
+        # Unlike the `django_client` fixture, a plain `Client()` sends no
+        # User-Agent header at all, matching the reported reproduction.
+        client = Client()
+        url = reverse("sign-in")
+
+        response = client.post(url, {"email": "user@plane.so", "password": "user@123"}, follow=False)
+
+        # Must redirect (successful sign-in), not 500.
+        assert response.status_code == 302
+        assert "error_code" not in response.url
+
+        setup_user.refresh_from_db()
+        assert setup_user.last_login_uagent == ""
+
     @pytest.mark.django_db
     def test_next_path_redirection(self, django_client, setup_user, setup_instance):
         """Test sign-in with next_path parameter"""