diff --git a/tests/conftest.py b/tests/conftest.py
index e757027..e931dd1 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -105,7 +105,7 @@ class Activations(Enum):
         RELU = "RELU"
         LINEAR = "LINEAR"
 
-    @dataclass
+    @dataclass(frozen=True)
     class TaskHyperParameters(TestSetup):
         """
         HyperParameters for a task-specific model
@@ -137,7 +137,7 @@ class Optimizers(Enum):
 
 @pytest.fixture
 def HyperParameters(TaskHyperParameters):
-    @dataclass
+    @dataclass(frozen=True)
     class HyperParameters(TestSetup):
         """Hyperparameters of a multi-headed model."""
 
diff --git a/tests/draccus_choice_plugins/gpt.py b/tests/draccus_choice_plugins/gpt.py
index 9e0f75a..107773e 100644
--- a/tests/draccus_choice_plugins/gpt.py
+++ b/tests/draccus_choice_plugins/gpt.py
@@ -4,6 +4,6 @@
 
 
 @ModelConfig.register_subclass("gpt")
-@dataclasses.dataclass
+@dataclasses.dataclass(frozen=True)
 class GptConfig(ModelConfig):
     attn_pdrop: float = 0.1
diff --git a/tests/draccus_choice_plugins/model_config.py b/tests/draccus_choice_plugins/model_config.py
index 7190c8f..5aba4c7 100644
--- a/tests/draccus_choice_plugins/model_config.py
+++ b/tests/draccus_choice_plugins/model_config.py
@@ -4,7 +4,7 @@
 from draccus.choice_types import PluginRegistry
 
 
-@dataclasses.dataclass
+@dataclasses.dataclass(frozen=True)
 class ModelConfig(PluginRegistry, discover_packages_path="tests.draccus_choice_plugins"):
     layers: int
 
@@ -14,6 +14,6 @@ def default_choice_name(cls) -> Optional[str]:
 
 
 @ModelConfig.register_subclass("mlp")
-@dataclasses.dataclass
+@dataclasses.dataclass(frozen=True)
 class MlpConfig(ModelConfig):
     hidden_size: int = 100
diff --git a/tests/test_argparse_choice_types_plugin.py b/tests/test_argparse_choice_types_plugin.py
index 68885a1..284bf4a 100644
--- a/tests/test_argparse_choice_types_plugin.py
+++ b/tests/test_argparse_choice_types_plugin.py
@@ -10,7 +10,7 @@
 
 
 def test_plugin_registry_argparse():
-    @dataclasses.dataclass
+    @dataclasses.dataclass(frozen=True)
     class Something(TestSetup):
         model: ModelConfig = MlpConfig(10, 5)