diff --git a/src/google/adk/evaluation/llm_as_judge.py b/src/google/adk/evaluation/llm_as_judge.py
index ce484ef58a7..9d6f59c7fb9 100644
--- a/src/google/adk/evaluation/llm_as_judge.py
+++ b/src/google/adk/evaluation/llm_as_judge.py
@@ -222,7 +222,11 @@ async def _evaluate_single_sample_with_sem(
               )
           ],
           config=self._judge_model_options.judge_model_config
-          or genai_types.GenerateContentConfig(),
+          or genai_types.GenerateContentConfig(
+              automatic_function_calling=genai_types.AutomaticFunctionCallingConfig(
+                  disable=True
+              )
+          ),
       )
       add_default_retry_options_if_not_present(llm_request)
       num_samples = self._judge_model_options.num_samples
diff --git a/tests/unittests/evaluation/test_llm_as_judge.py b/tests/unittests/evaluation/test_llm_as_judge.py
index d535febf4c9..f0b98f4065f 100644
--- a/tests/unittests/evaluation/test_llm_as_judge.py
+++ b/tests/unittests/evaluation/test_llm_as_judge.py
@@ -250,6 +250,59 @@ async def test_evaluate_invocations_with_mock(
   assert mock_llm_as_judge.aggregate_invocation_results.call_count == 1
 
 
+@pytest.mark.asyncio
+async def test_evaluate_invocations_default_config_disables_afc(
+    mock_judge_model, mocker
+):
+  # The default judge request must disable google-genai's automatic function
+  # calling, since the judge never calls tools and enabling it only produces
+  # a spurious AFC warning on every eval run.
+  judge = MockLlmAsJudge(
+      eval_metric=EvalMetric(
+          metric_name="test_metric",
+          threshold=0.5,
+          criterion=LlmAsAJudgeCriterion(
+              threshold=0.5,
+              judge_model_options=JudgeModelOptions(
+                  judge_model="gemini-2.5-flash",
+                  num_samples=1,
+              ),
+          ),
+      ),
+      criterion_type=LlmAsAJudgeCriterion,
+  )
+  judge._judge_model = mock_judge_model
+  captured_requests = []
+  original_generate_content_async = mock_judge_model.generate_content_async
+
+  def capturing_generate_content_async(llm_request):
+    captured_requests.append(llm_request)
+    return original_generate_content_async(llm_request)
+
+  judge._judge_model.generate_content_async = capturing_generate_content_async
+
+  actual_invocations = [
+      Invocation(
+          invocation_id="id1",
+          user_content=genai_types.Content(
+              parts=[genai_types.Part(text="user content 1")],
+              role="user",
+          ),
+          final_response=genai_types.Content(
+              parts=[genai_types.Part(text="final response 1")],
+              role="model",
+          ),
+      )
+  ]
+
+  await judge.evaluate_invocations(actual_invocations)
+
+  assert len(captured_requests) == 1
+  config = captured_requests[0].config
+  assert config.automatic_function_calling is not None
+  assert config.automatic_function_calling.disable is True
+
+
 @pytest.mark.asyncio
 async def test_evaluate_invocations_grades_criterion_only_metric(
     mock_judge_model,