diff --git a/devtools/prettier.py b/devtools/prettier.py
index d4e2b1f..1154668 100644
--- a/devtools/prettier.py
+++ b/devtools/prettier.py
@@ -230,9 +230,7 @@ def _format_bytearray(self, value: 'Any', _: str, indent_current: int, indent_ne
         self._str_lines(lines, indent_current, indent_new)
 
     def _format_dataclass(self, value: 'Any', _: str, indent_current: int, indent_new: int):
-        from dataclasses import asdict
-
-        self._format_fields(value, asdict(value).items(), indent_current, indent_new)
+        self._format_fields(value, value.__dict__.items(), indent_current, indent_new)
 
     def _format_sqlalchemy_class(self, value: 'Any', _: str, indent_current: int, indent_new: int):
         fields = [
diff --git a/tests/test_prettier.py b/tests/test_prettier.py
index 7ec2b66..6dea882 100644
--- a/tests/test_prettier.py
+++ b/tests/test_prettier.py
@@ -240,6 +240,29 @@ class FooDataclass:
 )"""
 
 
+def test_nested_dataclasses():
+    @dataclass
+    class FooDataclass:
+        x: int
+
+    @dataclass
+    class BarDataclass:
+        a: float
+        b: FooDataclass
+
+    f = FooDataclass(123)
+    b = BarDataclass(10.0, f)
+    v = pformat(b)
+    print(v)
+    assert v == """\
+BarDataclass(
+    a=10.0,
+    b=FooDataclass(
+        x=123,
+    ),
+)"""
+
+
 @pytest.mark.skipif(numpy is None, reason='numpy not installed')
 def test_indent_numpy():
     v = pformat({'numpy test': numpy.array(range(20))})