diff --git a/reasoning_gym/arithmetic/chain_sum.py b/reasoning_gym/arithmetic/chain_sum.py
index a9a99699..a2fa6157 100644
--- a/reasoning_gym/arithmetic/chain_sum.py
+++ b/reasoning_gym/arithmetic/chain_sum.py
@@ -20,6 +20,10 @@ class ChainSumConfig:
         assert self.max_terms >= self.min_terms, "max_terms must be >= min_terms"
         assert self.min_digits > 0, "min_digits must be positive"
         assert self.max_digits >= self.min_digits, "max_digits must be >= min_digits"
+        
+        # Validate digit ranges make sense
+        if self.min_digits > 1:
+            assert 10 ** (self.min_digits - 1) >= 1, "min_digits would result in invalid number range"
 
 
 class ChainSum:
@@ -64,8 +68,21 @@ class ChainSum:
         }
 
     def _generate_task(self, rng: Random, num_terms: int, num_digits: int) -> tuple[str, int]:
-        """Generate a chain sum task"""
-        constants = [rng.randint(0, 10**num_digits) for _ in range(num_terms)]
+        """Generate a chain sum task
+        
+        Args:
+            rng: Random number generator
+            num_terms: Number of terms in the expression
+            num_digits: Number of digits for each number
+            
+        Returns:
+            Tuple of (expression string, result integer)
+        """
+        # Generate numbers with at least min_digits
+        min_value = 10 ** (num_digits - 1)  # e.g., 100 for 3 digits
+        max_value = (10 ** num_digits) - 1   # e.g., 999 for 3 digits
+        
+        constants = [rng.randint(min_value, max_value) for _ in range(num_terms)]
         operators = [rng.choice(["+", "-"]) for _ in range(num_terms - 1)]
 
         # Build expression and compute result
diff --git a/tests/test_chain_sum.py b/tests/test_chain_sum.py
index f50e2335..75094a20 100644
--- a/tests/test_chain_sum.py
+++ b/tests/test_chain_sum.py
@@ -49,3 +49,27 @@ def test_chain_sum_items():
         # Verify the answer matches the expression
         answer = eval(expression)  # Safe here as we control the expression
         assert str(answer) == item["answer"]
+
+
+def test_chain_sum_number_ranges():
+    """Test that generated numbers respect digit constraints"""
+    config = ChainSumConfig(
+        min_terms=2,
+        max_terms=2,  # Fix to 2 terms for easier testing
+        min_digits=3,  # Should generate numbers >= 100
+        max_digits=3,  # Should generate numbers <= 999
+        size=50,
+        seed=42
+    )
+    dataset = ChainSum(config)
+    
+    for i in range(len(dataset)):
+        item = dataset[i]
+        expression = item["metadata"]["expression"]
+        
+        # Extract numbers from expression
+        numbers = [int(n) for n in expression.split() if n.isdigit()]
+        
+        # Verify each number is in the correct range
+        for num in numbers:
+            assert 100 <= num <= 999, f"Number {num} outside valid range for 3 digits"