diff --git a/src/cleveragents/skills/builtins/file_ops.py b/src/cleveragents/skills/builtins/file_ops.py
index 035994e74..b70086262 100644
--- a/src/cleveragents/skills/builtins/file_ops.py
+++ b/src/cleveragents/skills/builtins/file_ops.py
@@ -77,8 +77,12 @@ def validate_sandbox_path(path_str: str, sandbox_root: str | None = None) -> Pat
     root = root.resolve()
 
     target = (root / path_str).resolve()
-    if not str(target).startswith(str(root)):
-        raise ValueError(f"Path traversal detected: '{path_str}' escapes sandbox root")
+    try:
+        target.relative_to(root)
+    except ValueError as exc:
+        raise ValueError(
+            f"Path traversal detected: '{path_str}' escapes sandbox root",
+        ) from exc
     return target