diff --git a/tests/test_rewards.py b/tests/test_rewards.py
index f5fd582f68d..25beec5b573 100644
--- a/tests/test_rewards.py
+++ b/tests/test_rewards.py
@@ -161,6 +161,11 @@ def test_positive_max_penalty_raises(self):
         with pytest.raises(ValueError):
             get_repetition_penalty_reward(ngram_size=2, max_penalty=0.5)
 
+    @pytest.mark.parametrize("ngram_size", [0, -1])
+    def test_non_positive_ngram_size_raises(self, ngram_size):
+        with pytest.raises(ValueError):
+            get_repetition_penalty_reward(ngram_size=ngram_size, max_penalty=-1.0)
+
     def test_extra_kwargs_are_ignored(self):
         """Trainers pass prompts/completions/etc. as kwargs; the reward must accept and ignore them."""
         reward_fn = get_repetition_penalty_reward(ngram_size=2, max_penalty=-1.0)
diff --git a/trl/rewards/other_rewards.py b/trl/rewards/other_rewards.py
index 4848d10d183..dd30114593f 100644
--- a/trl/rewards/other_rewards.py
+++ b/trl/rewards/other_rewards.py
@@ -56,6 +56,8 @@ def get_repetition_penalty_reward(ngram_size: int = 3, max_penalty: float = -1.0
     """
     if max_penalty > 0:
         raise ValueError(f"max_penalty {max_penalty} should not be positive")
+    if ngram_size <= 0:
+        raise ValueError(f"ngram_size {ngram_size} should be greater than 0")
     return _RepetitionPenalty(ngram_size, max_penalty)