diff --git a/drf_spectacular/contrib/rest_polymorphic.py b/drf_spectacular/contrib/rest_polymorphic.py
index 1e725c52..fe0c64d6 100644
--- a/drf_spectacular/contrib/rest_polymorphic.py
+++ b/drf_spectacular/contrib/rest_polymorphic.py
@@ -42,8 +42,13 @@ def map_serializer(self, auto_schema, direction):
                     f'this might lead to code generation issues.'
                 )
 
+        one_of_list = []
+        for _, ref in sub_components:
+            if ref not in one_of_list:
+                one_of_list.append(ref)
+
         return {
-            'oneOf': [ref for _, ref in sub_components],
+            'oneOf': one_of_list,
             'discriminator': {
                 'propertyName': serializer.resource_type_field_name,
                 'mapping': {resource_type: ref['$ref'] for resource_type, ref in sub_components},
diff --git a/drf_spectacular/serializers.py b/drf_spectacular/serializers.py
index 8fafcb6d..5721abe7 100644
--- a/drf_spectacular/serializers.py
+++ b/drf_spectacular/serializers.py
@@ -20,8 +20,12 @@ def map_serializer(self, auto_schema, direction):
         if not self._has_discriminator():
             return {'oneOf': [schema for _, schema in sub_components]}
         else:
+            one_of_list = []
+            for _, schema in sub_components:
+                if schema not in one_of_list:
+                    one_of_list.append(schema)
             return {
-                'oneOf': [schema for _, schema in sub_components],
+                'oneOf': one_of_list,
                 'discriminator': {
                     'propertyName': self.target.resource_type_field_name,
                     'mapping': {resource_type: schema['$ref'] for resource_type, schema in sub_components}
diff --git a/tests/test_polymorphic.py b/tests/test_polymorphic.py
index 27b2cf9d..6f8bb349 100644
--- a/tests/test_polymorphic.py
+++ b/tests/test_polymorphic.py
@@ -1,3 +1,4 @@
+from random import choice
 from unittest import mock
 
 import pytest
@@ -324,6 +325,45 @@ def view_func(request, format=None):
     }
 
 
+def test_polymorphic_with_default_serializer(no_warnings):
+    class DefaultPersonSerializer(serializers.ModelSerializer):
+        type = serializers.SerializerMethodField()
+
+        class Meta:
+            model = NaturalPerson2
+            fields = ('id', 'type')
+
+        def get_type(self, obj) -> str:
+            return choice(['basic', 'simple'])
+
+    class XViewSet(viewsets.GenericViewSet):
+        @extend_schema(
+            responses=PolymorphicProxySerializer(
+                component_name='MetaPerson',
+                serializers={
+                    'natural': NaturalPersonSerializer,
+                    'basic': DefaultPersonSerializer,
+                    'simple': DefaultPersonSerializer,
+                },
+                resource_type_field_name='type',
+            )
+        )
+        def list(self, request, *args, **kwargs):
+            return Response({})  # pragma: no cover
+
+    schema = generate_schema('x', XViewSet)
+    components = schema['components']['schemas']
+    assert components['MetaPerson']['oneOf'] == [
+        {'$ref': '#/components/schemas/NaturalPerson'},
+        {'$ref': '#/components/schemas/DefaultPerson'}
+    ]
+    assert components['MetaPerson']['discriminator']['mapping'] == {
+        'natural': '#/components/schemas/NaturalPerson',
+        'basic': '#/components/schemas/DefaultPerson',
+        'simple': '#/components/schemas/DefaultPerson'
+    }
+
+
 def test_polymorphic_forced_many_false(no_warnings):
     class XViewSet(viewsets.GenericViewSet):
         @extend_schema(