diff --git a/google/cloud/aiplatform/vizier/pyvizier/proto_converters.py b/google/cloud/aiplatform/vizier/pyvizier/proto_converters.py
index 49862182c6..9072041e5d 100644
--- a/google/cloud/aiplatform/vizier/pyvizier/proto_converters.py
+++ b/google/cloud/aiplatform/vizier/pyvizier/proto_converters.py
@@ -222,15 +222,15 @@ def _set_child_parameter_configs(
                 )
             )
 
-            if parent_proto.HasField("discrete_value_spec"):
+            if "discrete_value_spec" in parent_proto:
                 conditional_parameter_spec.parent_discrete_values.values[
                     :
                 ] = parent_values
-            elif parent_proto.HasField("categorical_value_spec"):
+            elif "categorical_value_spec" in parent_proto:
                 conditional_parameter_spec.parent_categorical_values.values[
                     :
                 ] = parent_values
-            elif parent_proto.HasField("integer_value_spec"):
+            elif "integer_value_spec" in parent_proto:
                 conditional_parameter_spec.parent_int_values.values[:] = parent_values
             else:
                 raise ValueError("DOUBLE type cannot have child parameters")
diff --git a/tests/unit/aiplatform/test_vizier.py b/tests/unit/aiplatform/test_vizier.py
index 60c95a5baf..b8070e0bd1 100644
--- a/tests/unit/aiplatform/test_vizier.py
+++ b/tests/unit/aiplatform/test_vizier.py
@@ -987,11 +987,15 @@ def test_measurement_back_to_back_conversion(self):
 class TestParameterConfigConverterToProto:
     def test_discrete_config_to_proto(self):
         feasible_values = (-1, 3, 2)
+        child_parameter_config = pyvizier.ParameterConfig.factory(
+            "child", bounds=(-1.0, 1.0)
+        )
         parameter_config = pyvizier.ParameterConfig.factory(
             "name",
             feasible_values=feasible_values,
             scale_type=pyvizier.ScaleType.LOG,
             default_value=2,
+            children=[([-1], child_parameter_config)],
         )
 
         proto = proto_converters.ParameterConfigConverter.to_proto(parameter_config)
@@ -1002,6 +1006,43 @@ def test_discrete_config_to_proto(self):
             proto.scale_type
             == study_pb2.StudySpec.ParameterSpec.ScaleType.UNIT_LOG_SCALE
         )
+        assert len(proto.conditional_parameter_specs) == 1
+
+        spec = proto.conditional_parameter_specs[0]
+        assert spec.parameter_spec.parameter_id == "child"
+        assert spec.parameter_spec.double_value_spec.min_value == -1.0
+        assert spec.parameter_spec.double_value_spec.max_value == 1.0
+        assert len(spec.parent_discrete_values.values) == 1
+        assert spec.parent_discrete_values.values[0] == -1
+
+    def test_categorical_config_to_proto_with_children(self):
+        feasible_values = ("option_a", "option_b")
+        child_parameter_config = pyvizier.ParameterConfig.factory(
+            "child", bounds=(-1.0, 1.0)
+        )
+        parameter_config = pyvizier.ParameterConfig.factory(
+            "name",
+            feasible_values=feasible_values,
+            children=[(["option_a"], child_parameter_config)],
+        )
+        proto = proto_converters.ParameterConfigConverter.to_proto(parameter_config)
+        assert len(proto.conditional_parameter_specs) == 1
+        spec = proto.conditional_parameter_specs[0]
+        assert len(spec.parent_categorical_values.values) == 1
+        assert spec.parent_categorical_values.values[0] == "option_a"
+
+    def test_integer_config_to_proto_with_children(self):
+        child_parameter_config = pyvizier.ParameterConfig.factory(
+            "child", bounds=(-1.0, 1.0)
+        )
+        parameter_config = pyvizier.ParameterConfig.factory(
+            "name", bounds=(1, 10), children=[([6], child_parameter_config)]
+        )
+        proto = proto_converters.ParameterConfigConverter.to_proto(parameter_config)
+        assert len(proto.conditional_parameter_specs) == 1
+        spec = proto.conditional_parameter_specs[0]
+        assert len(spec.parent_int_values.values) == 1
+        assert spec.parent_int_values.values[0] == 6
 
 
 class TestParameterConfigConverterFromProto: