diff --git a/docs/changelog.md b/docs/changelog.md
index 535007d..3de5cdd 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -5,6 +5,8 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [UNRELEASED]
+### Fixed
+- generate the mapping for discriminator fields properly instead of showing a "null" value in the generated schema (#12).
 
 ## [0.12.0] - 2022-08-27
 ### Added
diff --git a/drf_standardized_errors/openapi.py b/drf_standardized_errors/openapi.py
index cd887a0..135bce9 100644
--- a/drf_standardized_errors/openapi.py
+++ b/drf_standardized_errors/openapi.py
@@ -19,6 +19,7 @@
 
 from .handler import exception_handler as standardized_errors_handler
 from .openapi_serializers import (
+    ClientErrorEnum,
     ErrorResponse401Serializer,
     ErrorResponse403Serializer,
     ErrorResponse404Serializer,
@@ -28,6 +29,7 @@
     ErrorResponse429Serializer,
     ErrorResponse500Serializer,
     ParseErrorResponseSerializer,
+    ValidationErrorEnum,
 )
 from .openapi_utils import (
     InputDataField,
@@ -253,12 +255,13 @@ def _get_http400_serializer(self):
         operation_id = self.get_operation_id()
         component_name = f"{camelize(operation_id)}ErrorResponse400"
 
-        http400_serializers = []
+        http400_serializers = {}
         if self._should_add_validation_error_response():
             serializer = self._get_serializer_for_validation_error_response()
-            http400_serializers.append(serializer)
+            http400_serializers[ValidationErrorEnum.VALIDATION_ERROR.value] = serializer
         if self._should_add_parse_error_response():
-            http400_serializers.append(ParseErrorResponseSerializer)
+            serializer = ParseErrorResponseSerializer
+            http400_serializers[ClientErrorEnum.CLIENT_ERROR.value] = serializer
 
         return PolymorphicProxySerializer(
             component_name=component_name,
diff --git a/drf_standardized_errors/openapi_utils.py b/drf_standardized_errors/openapi_utils.py
index 2cf9303..476660a 100644
--- a/drf_standardized_errors/openapi_utils.py
+++ b/drf_standardized_errors/openapi_utils.py
@@ -410,10 +410,10 @@ def get_validation_error_serializer(
 ):
     validation_error_component_name = f"{camelize(operation_id)}ValidationError"
     errors_component_name = f"{camelize(operation_id)}Error"
-    sub_serializers = [
-        get_error_serializer(operation_id, sfield.name, sfield.error_codes)
+    sub_serializers = {
+        sfield.name: get_error_serializer(operation_id, sfield.name, sfield.error_codes)
         for sfield in data_fields
-    ]
+    }
 
     class ValidationErrorSerializer(serializers.Serializer):
         type = serializers.ChoiceField(choices=ValidationErrorEnum.choices)
diff --git a/tests/test_openapi.py b/tests/test_openapi.py
index 2748e76..d61116d 100644
--- a/tests/test_openapi.py
+++ b/tests/test_openapi.py
@@ -84,6 +84,32 @@ def test_validation_error_for_unsafe_method():
     assert "400" in responses
 
 
+def test_discriminator_mapping_for_validation_serializer():
+    route = "validate/"
+    view = ValidationView.as_view()
+    schema = generate_view_schema(route, view)
+
+    discriminator = schema["components"]["schemas"]["ValidateCreateError"][
+        "discriminator"
+    ]
+    assert discriminator["propertyName"] == "attr"
+    mapping_fields = set(discriminator["mapping"])
+    assert mapping_fields == {"non_field_errors", "first_name"}
+
+
+def test_discriminator_mapping_for_http400_serializer():
+    route = "validate/"
+    view = ValidationView.as_view(parser_classes=[JSONParser])
+    schema = generate_view_schema(route, view)
+
+    discriminator = schema["components"]["schemas"]["ValidateCreateErrorResponse400"][
+        "discriminator"
+    ]
+    assert discriminator["propertyName"] == "type"
+    mapping_fields = set(discriminator["mapping"])
+    assert mapping_fields == {"validation_error", "client_error"}
+
+
 def test_no_validation_error_for_unsafe_method():
     route = "validate/"
     view = ValidationView.as_view(serializer_class=None)