diff --git a/src/OpenApi/src/Extensions/JsonNodeSchemaExtensions.cs b/src/OpenApi/src/Extensions/JsonNodeSchemaExtensions.cs
index 8e94a8e8b90c..7152e2d65f64 100644
--- a/src/OpenApi/src/Extensions/JsonNodeSchemaExtensions.cs
+++ b/src/OpenApi/src/Extensions/JsonNodeSchemaExtensions.cs
@@ -329,8 +329,19 @@ internal static void ApplyParameterInfo(this JsonNode schema, ApiParameterDescri
         {
             if (parameterInfo.HasDefaultValue)
             {
-                schema.ApplyDefaultValue(parameterInfo.DefaultValue, jsonTypeInfo);
+                var defaultValue = parameterInfo.DefaultValue;
+
+                // ParameterInfo.DefaultValue returns the underlying integral value for Nullable<TEnum> parameters,
+                // so convert it back to the enum type before serializing it.
+                if (defaultValue is not null
+                    && Nullable.GetUnderlyingType(parameterInfo.ParameterType) is { IsEnum: true } enumType)
+                {
+                    defaultValue = Enum.ToObject(enumType, defaultValue);
+                }
+
+                schema.ApplyDefaultValue(defaultValue, jsonTypeInfo);
             }
+
             else if (parameterInfo.GetCustomAttributes<DefaultValueAttribute>().LastOrDefault() is { } defaultValueAttribute)
             {
                 schema.ApplyDefaultValue(defaultValueAttribute.Value, jsonTypeInfo);
diff --git a/src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs b/src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs
index 559759290d8b..43e42d4127e5 100644
--- a/src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs
+++ b/src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs
@@ -163,6 +163,9 @@ await VerifyOpenApiDocument(builder, document =>
         [(TaskStatus status = TaskStatus.Canceled) => { }, (JsonNode defaultValue) => Assert.Equal(6, defaultValue.GetValue<int>())],
         // Default value for enums is serialized as string when a converter is registered.
         [(Status status = Status.Pending) => { }, (JsonNode defaultValue) => Assert.Equal("Pending", defaultValue.GetValue<string>())],
+        [(Status? status = Status.Pending) => { }, (JsonNode defaultValue) => Assert.Equal("Pending", defaultValue.GetValue<string>())],
+        [(TaskStatus? status = TaskStatus.Canceled) => { }, (JsonNode defaultValue) => Assert.Equal(6, defaultValue.GetValue<int>())],
+        [(Status? status = null) => { }, (JsonNode defaultValue) => Assert.True(defaultValue is null)],
         [([DefaultValue(2)] int id) => { }, (JsonNode defaultValue) => Assert.Equal(2, defaultValue.GetValue<int>())],
         [([DefaultValue(3f)] float id) => { }, (JsonNode defaultValue) => Assert.Equal(3, defaultValue.GetValue<int>())],
         [([DefaultValue("test")] string id) => { }, (JsonNode defaultValue) => Assert.Equal("test", defaultValue.GetValue<string>())],
@@ -198,6 +201,19 @@ await VerifyOpenApiDocument(builder, document =>
     }
 #nullable restore
 
+    [Fact]
+    public async Task GetOpenApiRequestBody_HandlesNullableEnumBodyParameterWithDefaultValue()
+    {
+        var builder = CreateBuilder();
+        builder.MapPost("/api/body", ([FromBody] Status? status = Status.Pending) => status);
+
+        await VerifyOpenApiDocument(builder, document =>
+        {
+            var op = document.Paths["/api/body"].Operations[HttpMethod.Post];
+            Assert.NotNull(op.RequestBody);
+        });
+    }
+
     [Fact]
     public async Task GetOpenApiParameters_HandlesEnumParameterWithoutConverter()
     {