diff --git a/RELEASE_NOTES.rst b/RELEASE_NOTES.rst
index 73fcf6ee3..87101be7f 100644
--- a/RELEASE_NOTES.rst
+++ b/RELEASE_NOTES.rst
@@ -20,6 +20,12 @@ unreleased [2.x]
   just "-m qcX" or "-m clock" (#290).
 
 
+unreleased [1.0rc3]
+-------------------
+
+* The HDF5 format has changed. The datasets are located in the subgroup ``datasets``.
+
+
 1.0rc2
 ------
 
diff --git a/artiq/master/worker_db.py b/artiq/master/worker_db.py
index eadc0a0b9..16046cd26 100644
--- a/artiq/master/worker_db.py
+++ b/artiq/master/worker_db.py
@@ -250,4 +250,5 @@ class DatasetManager:
             return self.ddb.get(key)
 
     def write_hdf5(self, f):
-        result_dict_to_hdf5(f, self.local)
+        g = f.create_group("datasets")
+        result_dict_to_hdf5(g, self.local)
diff --git a/artiq/master/worker_impl.py b/artiq/master/worker_impl.py
index 6bb1aaf4d..a6258b94f 100644
--- a/artiq/master/worker_impl.py
+++ b/artiq/master/worker_impl.py
@@ -218,14 +218,11 @@ def main():
                 exp_inst.analyze()
                 put_object({"action": "completed"})
             elif action == "write_results":
-                f = get_hdf5_output(start_time, rid, exp.__name__)
-                try:
+                with get_hdf5_output(start_time, rid, exp.__name__) as f:
                     dataset_mgr.write_hdf5(f)
-                    string_to_hdf5(f, "artiq_version", artiq_version)
+                    string_to_hdf5(f, "version", artiq_version)
                     if "repo_rev" in expid:
                         string_to_hdf5(f, "repo_rev", expid["repo_rev"])
-                finally:
-                    f.close()
                 put_object({"action": "completed"})
             elif action == "examine":
                 examine(ExamineDeviceMgr, ParentDatasetDB, obj["file"])