diff --git a/src/uproot/models/RNTuple.py b/src/uproot/models/RNTuple.py
index ef65f2171..f38e00a02 100644
--- a/src/uproot/models/RNTuple.py
+++ b/src/uproot/models/RNTuple.py
@@ -30,7 +30,7 @@
 _rntuple_cluster_summary_format = struct.Struct("<QQ")
 _rntuple_checksum_format = struct.Struct("<Q")
 _rntuple_envlink_size_format = struct.Struct("<Q")
-_rntuple_page_num_elements_format = struct.Struct("<I")
+_rntuple_page_num_elements_format = struct.Struct("<i")
 _rntuple_column_group_id_format = struct.Struct("<I")
 _rntuple_first_ele_index_format = struct.Struct("<I")
 
@@ -338,15 +338,26 @@ def field_form(self, this_id, seen):
             structural_role == uproot.const.rntuple_role_leaf
             and this_record.repetition == 0
         ):
+            # deal with std::atomic
+            # they have no associated column, but exactly one subfield containing the underlying data
+            tmp_id = self._alias_columns_dict.get(this_id, this_id)
+            if (
+                tmp_id not in self._column_records_dict
+                and len(self._related_ids[tmp_id]) == 1
+            ):
+                this_id = self._related_ids[tmp_id][0]
+                seen.add(this_id)
             # base case of recursion
             # n.b. the split may happen in column
             return self.col_form(this_id)
         elif structural_role == uproot.const.rntuple_role_leaf:
-            # std::array it only has one child
             if this_id in self._related_ids:
+                # std::array has only one subfield
                 child_id = self._related_ids[this_id][0]
-
-            inner = self.field_form(child_id, seen)
+                inner = self.field_form(child_id, seen)
+            else:
+                # std::bitset has no subfields, so we use it directly
+                inner = self.col_form(this_id)
             keyname = f"RegularForm-{this_id}"
             return ak.forms.RegularForm(inner, this_record.repetition, form_key=keyname)
         elif structural_role == uproot.const.rntuple_role_vector:
@@ -387,7 +398,10 @@ def field_form(self, this_id, seen):
             if this_id in self._related_ids:
                 newids = self._related_ids[this_id]
             recordlist = [self.field_form(i, seen) for i in newids]
-            return ak.forms.UnionForm("i8", "i64", recordlist, form_key=keyname)
+            inner = ak.forms.UnionForm(
+                "i8", "i64", recordlist, form_key=keyname + "-union"
+            )
+            return ak.forms.IndexedOptionForm("i64", inner, form_key=keyname)
         else:
             # everything should recurse above this branch
             raise AssertionError("this should be unreachable")
@@ -538,13 +552,15 @@ def arrays(
             [c.num_entries for c in clusters[start_cluster_idx:stop_cluster_idx]]
         )
 
-        form = self.to_akform().select_columns(filter_names)
+        form = self.to_akform().select_columns(
+            filter_names, prune_unions_and_records=False
+        )
         # only read columns mentioned in the awkward form
         target_cols = []
         container_dict = {}
         _recursive_find(form, target_cols)
         for key in target_cols:
-            if "column" in key:
+            if "column" in key and "union" not in key:
                 key_nr = int(key.split("-")[1])
                 dtype_byte = self.column_records[key_nr].type
                 content = self.read_col_pages(
@@ -556,8 +572,20 @@ def arrays(
                     content = numpy.diff(content)
                 if dtype_byte == uproot.const.rntuple_col_type_to_num_dict["switch"]:
                     kindex, tags = _split_switch_bits(content)
-                    container_dict[f"{key}-index"] = kindex
-                    container_dict[f"{key}-tags"] = tags
+                    # Find invalid variants and adjust buffers accordingly
+                    invalid = numpy.flatnonzero(tags == -1)
+                    if len(invalid) > 0:
+                        kindex = numpy.delete(kindex, invalid)
+                        tags = numpy.delete(tags, invalid)
+                        invalid -= numpy.arange(len(invalid))
+                        optional_index = numpy.insert(
+                            numpy.arange(len(kindex), dtype=numpy.int64), invalid, -1
+                        )
+                    else:
+                        optional_index = numpy.arange(len(kindex), dtype=numpy.int64)
+                    container_dict[f"{key}-index"] = optional_index
+                    container_dict[f"{key}-union-index"] = kindex
+                    container_dict[f"{key}-union-tags"] = tags
                 else:
                     # don't distinguish data and offsets
                     container_dict[f"{key}-data"] = content
@@ -565,9 +593,9 @@ def arrays(
         cluster_offset = cluster_starts[start_cluster_idx]
         entry_start -= cluster_offset
         entry_stop -= cluster_offset
-        return ak.from_buffers(form, cluster_num_entries, container_dict)[
-            entry_start:entry_stop
-        ]
+        return ak.from_buffers(
+            form, cluster_num_entries, container_dict, allow_noncanonical_form=True
+        )[entry_start:entry_stop]
 
 
 # Supporting function and classes
@@ -592,9 +620,9 @@ def _recursive_find(form, res):
 class PageDescription:
     def read(self, chunk, cursor, context):
         out = MetaData(type(self).__name__)
-        out.num_elements = cursor.field(
-            chunk, _rntuple_page_num_elements_format, context
-        )
+        num_elements = cursor.field(chunk, _rntuple_page_num_elements_format, context)
+        out.has_checksum = num_elements < 0
+        out.num_elements = abs(num_elements)
         out.locator = LocatorReader().read(chunk, cursor, context)
         return out
 
diff --git a/tests/test_1223_more_rntuple_types.py b/tests/test_1223_more_rntuple_types.py
new file mode 100644
index 000000000..686d82afb
--- /dev/null
+++ b/tests/test_1223_more_rntuple_types.py
@@ -0,0 +1,87 @@
+# BSD 3-Clause License; see https://github.com/scikit-hep/uproot5/blob/main/LICENSE
+
+import pytest
+import skhep_testdata
+
+import uproot
+
+
+def test_atomic():
+    filename = skhep_testdata.data_path("test_ntuple_atomic_bitset.root")
+    with uproot.open(filename) as f:
+        obj = f["ntuple"]
+
+        a = obj.arrays("atomic_int")
+
+        assert a.atomic_int.tolist() == [1, 2, 3]
+
+
+def test_bitset():
+    filename = skhep_testdata.data_path("test_ntuple_atomic_bitset.root")
+    with uproot.open(filename) as f:
+        obj = f["ntuple"]
+
+        a = obj.arrays("bitset")
+
+        assert len(a.bitset) == 3
+        assert len(a.bitset[0]) == 42
+        assert a.bitset[0].tolist()[:6] == [0, 1, 0, 1, 0, 1]
+        assert all(a.bitset[0][6:] == 0)
+        assert a.bitset[1].tolist()[:16] == [
+            0,
+            1,
+            0,
+            1,
+            0,
+            1,
+            0,
+            1,
+            0,
+            1,
+            0,
+            1,
+            0,
+            1,
+            0,
+            1,
+        ]
+        assert all(a.bitset[1][16:] == 0)
+        assert a.bitset[2].tolist()[:16] == [
+            0,
+            0,
+            0,
+            1,
+            0,
+            0,
+            0,
+            1,
+            0,
+            0,
+            0,
+            1,
+            0,
+            0,
+            0,
+            1,
+        ]
+        assert all(a.bitset[2][16:] == 0)
+
+
+def test_empty_struct():
+    filename = skhep_testdata.data_path("test_ntuple_emptystruct_invalidvar.root")
+    with uproot.open(filename) as f:
+        obj = f["ntuple"]
+
+        a = obj.arrays("empty_struct")
+
+        assert a.empty_struct.tolist() == [{}, {}, {}]
+
+
+def test_invalid_variant():
+    filename = skhep_testdata.data_path("test_ntuple_emptystruct_invalidvar.root")
+    with uproot.open(filename) as f:
+        obj = f["ntuple"]
+
+        a = obj.arrays("variant")
+
+        assert a.variant.tolist() == [1, 1, None]