diff --git a/reasoning_gym/arithmetic/chain_sum.py b/reasoning_gym/arithmetic/chain_sum.py
index ca53c1fa..ea41c157 100644
--- a/reasoning_gym/arithmetic/chain_sum.py
+++ b/reasoning_gym/arithmetic/chain_sum.py
@@ -1,5 +1,5 @@
 from dataclasses import dataclass
-from random import Random
+import random
 from typing import Optional
 
 
@@ -33,7 +33,7 @@ class ChainSum:
         self.config = config
         self.config.validate()
         # Generate base seed if none provided
-        self.seed = config.seed if config.seed is not None else Random().randint(0, 2**32)
+        self.seed = config.seed if config.seed is not None else random.randint(0, 2**32)
         
     def __len__(self) -> int:
         return self.config.size
@@ -50,8 +50,8 @@ class ChainSum:
                 - answer: str, the ground truth result
                 - metadata: dict with generation parameters
         """
-        # Create deterministic RNG directly from base seed and idx
-        item_rng = Random(self.seed + idx)
+        # Create deterministic RNG from base seed and idx
+        item_rng = random.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)
@@ -68,7 +68,7 @@ class ChainSum:
             }
         }
 
-    def _generate_task(self, rng: Random, num_terms: int, num_digits: int) -> tuple[str, int]:
+    def _generate_task(self, rng: random.Random, num_terms: int, num_digits: int) -> tuple[str, int]:
         """Generate a chain sum task
         
         Args: