diff --git a/reasoning_gym/arithmetic/basic_arithmetic.py b/reasoning_gym/arithmetic/basic_arithmetic.py
index 9a97f35b..dc5ff890 100644
--- a/reasoning_gym/arithmetic/basic_arithmetic.py
+++ b/reasoning_gym/arithmetic/basic_arithmetic.py
@@ -34,7 +34,8 @@ class ArithmeticDataset:
     def __init__(self, config: ArithmeticDatasetConfig):
         self.config = config
         self.config.validate()
-        self.rng = Random(config.seed)
+        # Generate base seed if none provided
+        self.seed = config.seed if config.seed is not None else Random().randint(0, 2**32)
         
     def __len__(self) -> int:
         return self.config.size
@@ -51,8 +52,8 @@ class ArithmeticDataset:
                 - answer: str, the ground truth result
                 - metadata: dict with generation parameters
         """
-        # Use seed derived from idx for deterministic generation
-        item_rng = Random(self.rng.randint(0, 2**32) + idx)
+        # Create deterministic RNG from base seed and idx
+        item_rng = Random(self.seed + idx)
         
         num_terms = item_rng.randint(self.config.min_terms, self.config.max_terms)
         num_digits = item_rng.randint(self.config.min_digits, self.config.max_digits)
@@ -165,4 +166,6 @@ class ArithmeticDataset:
                 "Solve {0}",
                 "Evaluate the expression: {0}"
             ]
-            return self.rng.choice(templates).format(expression)
+            # Use deterministic RNG for template selection
+            template_rng = Random(self.seed)
+            return template_rng.choice(templates).format(expression)