diff --git a/reasoning_gym/arithmetic/basic_arithmetic.py b/reasoning_gym/arithmetic/basic_arithmetic.py
index 7ea7027a..26758a74 100644
--- a/reasoning_gym/arithmetic/basic_arithmetic.py
+++ b/reasoning_gym/arithmetic/basic_arithmetic.py
@@ -17,6 +17,7 @@ class ArithmeticDatasetConfig:
     seed: Optional[int] = None
     size: int = 500  # Virtual dataset size
     format_style: Literal["simple", "natural"] = "simple"
+    whitespace: Literal["no_space", "single", "random"] = "single"  # Whitespace style between terms
 
     def validate(self):
         """Validate configuration parameters"""
@@ -104,14 +105,18 @@ class ArithmeticDataset:
 
         add_terms(num_terms)
 
-        # Add at most one random space between parts
-        space_parts = []
-        for p in parts:
-            if rng.random() < 0.15:
-                space_parts.append(" ")
-            space_parts.append(p)
-
-        expression = " ".join(space_parts).strip()
+        # Add whitespace according to config
+        if self.config.whitespace == "no_space":
+            expression = "".join(parts)
+        elif self.config.whitespace == "single":
+            expression = " ".join(parts)
+        else:  # random
+            space_parts = []
+            for p in parts:
+                if rng.random() < 0.15:
+                    space_parts.append(" ")
+                space_parts.append(p)
+            expression = "".join(space_parts).strip()
         result = eval(expression)  # Note: eval is safe here as we control the input
 
         return expression, result
@@ -176,6 +181,7 @@ def arithmetic_dataset(
     seed: Optional[int] = None,
     size: int = 500,
     format_style: Literal["simple", "natural"] = "simple",
+    whitespace: Literal["no_space", "single", "random"] = "single",
 ) -> ArithmeticDataset:
     """Create an ArithmeticDataset with the given configuration.
 
@@ -205,5 +211,6 @@ def arithmetic_dataset(
         seed=seed,
         size=size,
         format_style=format_style,
+        whitespace=whitespace,
     )
     return ArithmeticDataset(config)