diff --git a/bench_runner/result.py b/bench_runner/result.py
index f561126..240c5cb 100644
--- a/bench_runner/result.py
+++ b/bench_runner/result.py
@@ -48,9 +48,9 @@ def _clean(string: str) -> str:
     """
     Clean an arbitrary string to be suitable for a filename.
 
-    It can't contain dashes, since dashes are used as a delimiter.
+    Dashes delimit filename fields, and slashes would create subdirectories.
     """
-    return string.replace("-", "_")
+    return string.replace("-", "_").replace("/", "_")
 
 
 def _clean_for_url(string: str) -> str:
diff --git a/tests/test_result.py b/tests/test_result.py
index d878b79..ecdcd12 100644
--- a/tests/test_result.py
+++ b/tests/test_result.py
@@ -122,3 +122,7 @@ def gethostname(*args):
         f"bm-20221119-{platform.system().lower()}-{platform.machine().lower()}"
         f"-my%2dfork-9d38120e335357a3b294-{platform.python_version()}-b7e4f1d.json"
     )
+
+    result = mod_result.Result.from_scratch(python, "my-fork", "jit/free-threading")
+    assert result.ref == "jit_free_threading"
+    assert result.filename.parent.parent == Path("results")