diff --git a/serve/mlc_serve/engine/sampling_params.py b/serve/mlc_serve/engine/sampling_params.py
index 3d8db5a2ea..1d210e38ed 100644
--- a/serve/mlc_serve/engine/sampling_params.py
+++ b/serve/mlc_serve/engine/sampling_params.py
@@ -88,6 +88,8 @@ def __post_init__(self):
             self._verify_greedy_sampling()
         if not self.logprobs:
             self.top_logprobs = 0
+        if self.top_k == -1:
+            self.top_k = self.vocab_size
 
     def verify(self) -> None:
         if not -2.0 <= self.presence_penalty <= 2.0:
diff --git a/serve/tests/unittest/test_sampler.py b/serve/tests/unittest/test_sampler.py
index 7b0e892cd6..d8fa27c3a2 100644
--- a/serve/tests/unittest/test_sampler.py
+++ b/serve/tests/unittest/test_sampler.py
@@ -227,7 +227,8 @@ def _get_prompt_mask(vocab_size: int, batch_size: int) -> List[List[bool]]:
             ],
         )
 
-def test_penalties():
+@pytest.mark.parametrize("batch_size", [1, 4])
+def test_penalties(batch_size: int):
     def _prepare_metadata(past_output_tokens):
         count_map = []
         for past_output_tokens_per_req in past_output_tokens:
@@ -256,61 +257,64 @@ def _get_expected_result(
             temperature = temperatures[i]
             if temperature < SAMPLING_EPS:
                 temperature = 1.0
-            rp_pen = torch.where(
+            rep_pen = torch.where(
                 mask[i],
                 repetition_penalties[i],
                 1.0
             )
+            expected[i] = torch.where(
+                expected[i] > 0, expected[i] / rep_pen, expected[i] * rep_pen
+            )
             expected[i] = (
                (expected[i]
                 - count_map[i] * frequency_penalties[i]
                 - mask[i] * presence_penalties[i])
-                / (temperature * rp_pen)
+                / temperature
             )
         return expected
 
-    for batch_size in [1, 4, 8]:
-        shape = (batch_size, vocab_size)
-        logits = torch.rand(shape, dtype=dtype, device=dev)
-        past_output_tokens = [[2, 2, 2, 3, 5]] * batch_size
-        count_map, mask = _prepare_metadata(past_output_tokens)
-
-        temperatures = [0.0, 0.5, 1.0, 1.5, 2.0]
-        presence_penalties = [-2.0, -1.4, -0.8, 0.0, 0.5, 1.0, 1.5, 2.0]
-        frequency_penalties = [-2.0, -1.4, -0.8, 0.0, 0.5, 1.0, 1.5, 2.0]
-        repetition_penalties = [0.1, 0.6, 1.0, 1.5, 1.8, 2.1, 2.5, 3.0]
-        for batch_params in permutations(
-            product(
-                temperatures,
-                repetition_penalties,
-                presence_penalties,
-                frequency_penalties
-            ),
-            batch_size
-        ):
-            sampling_params = [
-                SamplingParams(
-                    temperature=temp,
-                    repetition_penalty=rep_pen,
-                    presence_penalty=pr_pen,
-                    frequency_penalty=fr_pen
-                )
-                for temp, rep_pen, pr_pen, fr_pen in batch_params
-            ]
-            expected = _get_expected_result(
-                logits,
-                count_map,
-                mask,
-                [temp for temp, _, _, _ in batch_params],
-                [rep_pen for _, rep_pen, _, _ in batch_params],
-                [pr_pen for _, _, pr_pen, _ in batch_params],
-                [fr_pen for _, _, _, fr_pen in batch_params],
-            )
-            sampling_state = get_sampling_state(
-                sampling_params, past_output_tokens=past_output_tokens
+    shape = (batch_size, vocab_size)
+    logits = torch.rand(shape, dtype=dtype, device=dev)
+    past_output_tokens = [[2, 2, 2, 3, 5]] * batch_size
+    count_map, mask = _prepare_metadata(past_output_tokens)
+
+    temperatures = [0.6]
+    presence_penalties = [-2.0, 2.0]
+    frequency_penalties = [-2.0, 2.0]
+    repetition_penalties = [0.4, 1.0]
+    for batch_params in permutations(
+        product(
+            temperatures,
+            repetition_penalties,
+            presence_penalties,
+            frequency_penalties
+        ),
+        batch_size
+    ):
+        print(batch_params)
+        sampling_params = [
+            SamplingParams(
+                temperature=temp,
+                repetition_penalty=rep_pen,
+                presence_penalty=pr_pen,
+                frequency_penalty=fr_pen,
             )
-            new_logits = adjust_logits(logits, sampling_state, vocab_size)
-            assert torch.allclose(expected, new_logits), f"{torch.isclose(expected, new_logits)}, {batch_params}"
+            for temp, rep_pen, pr_pen, fr_pen in batch_params
+        ]
+        expected = _get_expected_result(
+            logits,
+            count_map,
+            mask,
+            [temp for temp, _, _, _ in batch_params],
+            [rep_pen for _, rep_pen, _, _ in batch_params],
+            [pr_pen for _, _, pr_pen, _ in batch_params],
+            [fr_pen for _, _, _, fr_pen in batch_params],
+        )
+        sampling_state = get_sampling_state(
+            sampling_params, past_output_tokens=past_output_tokens
+        )
+        new_logits = adjust_logits(logits, sampling_state, vocab_size)
+        assert torch.allclose(expected, new_logits), f"{torch.isclose(expected, new_logits)}, {batch_params}"
 
 
 def test_top_p_top_k_checker():