diff --git a/docs/generators/aspnetcore.md b/docs/generators/aspnetcore.md
index 14d54f778d4..d7e282c8279 100644
--- a/docs/generators/aspnetcore.md
+++ b/docs/generators/aspnetcore.md
@@ -19,7 +19,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |licenseUrl|The URL of the license| |http://localhost|
 |modelClassModifier|Model Class Modifier can be nothing or partial| |partial|
 |newtonsoftVersion|Version for Microsoft.AspNetCore.Mvc.NewtonsoftJson for ASP.NET Core 3.0+| |3.0.0|
-|nullableReferenceTypes|Annotate Project with <Nullable>annotations</Nullable> and use ? annotation on all nullable attributes. Only supported on C# 8 / ASP.NET Core 3.0 or newer.| |false|
+|nullableReferenceTypes|Use nullable annotations in the project. Only supported on C# 8 / ASP.NET Core 3.0 or newer.| |false|
 |operationIsAsync|Set methods to async or sync (default).| |false|
 |operationModifier|Operation Modifier can be virtual or abstract|<dl><dt>**virtual**</dt><dd>Keep method virtual</dd><dt>**abstract**</dt><dd>Make method abstract</dd></dl>|virtual|
 |operationResultTask|Set methods result to Task&lt;&gt;.| |false|
diff --git a/docs/generators/csharp-netcore.md b/docs/generators/csharp-netcore.md
index 0887dcbfeca..e7b92383494 100644
--- a/docs/generators/csharp-netcore.md
+++ b/docs/generators/csharp-netcore.md
@@ -17,6 +17,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |modelPropertyNaming|Naming convention for the property: 'camelCase', 'PascalCase', 'snake_case' and 'original', which keeps the original name| |PascalCase|
 |netCoreProjectFile|Use the new format (.NET Core) for .NET project files (.csproj).| |false|
 |nonPublicApi|Generates code with reduced access modifiers; allows embedding elsewhere without exposing non-public API calls to consumers.| |false|
+|nullableReferenceTypes|Use nullable annotations in the project. Only supported on C# 8 / ASP.NET Core 3.0 or newer.| |false|
 |optionalAssemblyInfo|Generate AssemblyInfo.cs.| |true|
 |optionalEmitDefaultValues|Set DataMember's EmitDefaultValue.| |false|
 |optionalMethodArgument|C# Optional method argument, e.g. void square(int x=10) (.net 4.0+ only).| |true|
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenConstants.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenConstants.java
index b8caef27e9f..72a3d57ce0f 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenConstants.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenConstants.java
@@ -211,6 +211,9 @@ public class CodegenConstants {
     public static final String DOTNET_FRAMEWORK = "targetFramework";
     public static final String DOTNET_FRAMEWORK_DESC = "The target .NET framework version. To target multiple frameworks, use `;` as the separator, e.g. `netstandard2.1;netcoreapp3.0`";
 
+    public static final String NULLABLE_REFERENCE_TYPES = "nullableReferenceTypes";
+    public static final String NULLABLE_REFERENCE_TYPES_DESC = "Use nullable annotations in the project. Only supported on C# 8 / ASP.NET Core 3.0 or newer.";
+
     public static final String TEMPLATING_ENGINE = "templatingEngine";
     public static final String TEMPLATING_ENGINE_DESC = "The templating engine plugin to use: \"mustache\" (default) or \"handlebars\" (beta)";
 
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java
index 883f6cb078b..b939826b1ff 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java
@@ -47,6 +47,7 @@ public abstract class AbstractCSharpCodegen extends DefaultCodegen implements Co
     protected boolean useCollection = false;
     protected boolean returnICollection = false;
     protected boolean netCoreProjectFileFlag = false;
+    protected boolean nullReferenceTypesFlag = false;
 
     protected String modelPropertyNaming = CodegenConstants.MODEL_PROPERTY_NAMING_TYPE.PascalCase.name();
 
@@ -356,6 +357,12 @@ public abstract class AbstractCSharpCodegen extends DefaultCodegen implements Co
             additionalProperties.put(CodegenConstants.NETCORE_PROJECT_FILE, netCoreProjectFileFlag);
         }
 
+        if (additionalProperties.containsKey(CodegenConstants.NULLABLE_REFERENCE_TYPES)) {
+            setNullableReferenceTypes(convertPropertyToBooleanAndWriteBack(CodegenConstants.NULLABLE_REFERENCE_TYPES));
+        } else {
+            additionalProperties.put(CodegenConstants.NULLABLE_REFERENCE_TYPES, nullReferenceTypesFlag);
+        }
+
         if (additionalProperties.containsKey(CodegenConstants.INTERFACE_PREFIX)) {
             String useInterfacePrefix = additionalProperties.get(CodegenConstants.INTERFACE_PREFIX).toString();
             if ("false".equals(useInterfacePrefix.toLowerCase(Locale.ROOT))) {
@@ -1112,6 +1119,13 @@ public abstract class AbstractCSharpCodegen extends DefaultCodegen implements Co
         return interfacePrefix;
     }
 
+    public void setNullableReferenceTypes(final Boolean nullReferenceTypesFlag){
+        this.nullReferenceTypesFlag = nullReferenceTypesFlag;
+        if (nullReferenceTypesFlag == true){
+            this.nullableType.add("string");
+        }
+    }
+
     public void setInterfacePrefix(final String interfacePrefix) {
         this.interfacePrefix = interfacePrefix;
     }
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AspNetCoreServerCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AspNetCoreServerCodegen.java
index ca50b0ff1f4..16957ff6b3b 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AspNetCoreServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AspNetCoreServerCodegen.java
@@ -60,7 +60,6 @@ public class AspNetCoreServerCodegen extends AbstractCSharpCodegen {
     public static final String USE_NEWTONSOFT = "useNewtonsoft";
     public static final String USE_DEFAULT_ROUTING = "useDefaultRouting";
     public static final String NEWTONSOFT_VERSION = "newtonsoftVersion";
-    public static final String NULLABLE_REFERENCE_TYPES = "nullableReferenceTypes";
 
     private String packageGuid = "{" + randomUUID().toString().toUpperCase(Locale.ROOT) + "}";
     private String userSecretsGuid = randomUUID().toString();
@@ -85,7 +84,6 @@ public class AspNetCoreServerCodegen extends AbstractCSharpCodegen {
     private boolean useFrameworkReference = false;
     private boolean useNewtonsoft = true;
     private boolean useDefaultRouting = true;
-    private boolean nullableReferenceTypes = false;
     private String newtonsoftVersion = "3.0.0";
 
     public AspNetCoreServerCodegen() {
@@ -211,6 +209,10 @@ public class AspNetCoreServerCodegen extends AbstractCSharpCodegen {
         cliOptions.add(swashbuckleVersion);
 
         // CLI Switches
+        addSwitch(CodegenConstants.NULLABLE_REFERENCE_TYPES,
+                CodegenConstants.NULLABLE_REFERENCE_TYPES_DESC,
+                this.nullReferenceTypesFlag);
+
         addSwitch(CodegenConstants.SORT_PARAMS_BY_REQUIRED_FLAG,
                 CodegenConstants.SORT_PARAMS_BY_REQUIRED_FLAG_DESC,
                 sortParamsByRequiredFlag);
@@ -251,11 +253,6 @@ public class AspNetCoreServerCodegen extends AbstractCSharpCodegen {
                 "Use default routing for the ASP.NET Core version.",
                 useDefaultRouting);
 
-        addSwitch(NULLABLE_REFERENCE_TYPES,
-                "Annotate Project with <Nullable>annotations</Nullable> and use ? annotation on all nullable attributes. " +
-                          "Only supported on C# 8 / ASP.NET Core 3.0 or newer.",
-                nullableReferenceTypes);
-
         addOption(CodegenConstants.ENUM_NAME_SUFFIX,
                 CodegenConstants.ENUM_NAME_SUFFIX_DESC,
                 enumNameSuffix);
@@ -373,7 +370,6 @@ public class AspNetCoreServerCodegen extends AbstractCSharpCodegen {
         setIsFramework();
         setUseNewtonsoft();
         setUseEndpointRouting();
-        setNullableReferenceTypes();
 
         supportingFiles.add(new SupportingFile("build.sh.mustache", "", "build.sh"));
         supportingFiles.add(new SupportingFile("build.bat.mustache", "", "build.bat"));
@@ -528,7 +524,7 @@ public class AspNetCoreServerCodegen extends AbstractCSharpCodegen {
     @Override
     public String getNullableType(Schema p, String type) {
         if (languageSpecificPrimitives.contains(type)) {
-            if (isSupportNullable() && ModelUtils.isNullable(p) && (nullableType.contains(type) || nullableReferenceTypes)) {
+            if (isSupportNullable() && ModelUtils.isNullable(p) && (nullableType.contains(type) || nullReferenceTypesFlag)) {
                 return type + "?";
             } else {
                 return type;
@@ -657,20 +653,6 @@ public class AspNetCoreServerCodegen extends AbstractCSharpCodegen {
         }
     }
 
-    private void setNullableReferenceTypes() {
-        if (additionalProperties.containsKey(NULLABLE_REFERENCE_TYPES)) {
-            if (aspnetCoreVersion.getOptValue().startsWith("2.")) {
-                LOGGER.warn("Nullable annotation are not supported in ASP.NET core version 2. Setting {} to false",
-                        NULLABLE_REFERENCE_TYPES);
-                additionalProperties.put(NULLABLE_REFERENCE_TYPES, false);
-            } else {
-                nullableReferenceTypes = convertPropertyToBooleanAndWriteBack(NULLABLE_REFERENCE_TYPES);
-            }
-        } else {
-            additionalProperties.put(NULLABLE_REFERENCE_TYPES, nullableReferenceTypes);
-        }
-    }
-
     private void setOperationIsAsync() {
         if (isLibrary) {
             operationIsAsync = false;
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpNetCoreClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpNetCoreClientCodegen.java
index 2b0a5fe068d..d0bb7c24b6e 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpNetCoreClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpNetCoreClientCodegen.java
@@ -230,6 +230,10 @@ public class CSharpNetCoreClientCodegen extends AbstractCSharpCodegen {
         cliOptions.add(modelPropertyNaming.defaultValue("PascalCase"));
 
         // CLI Switches
+        addSwitch(CodegenConstants.NULLABLE_REFERENCE_TYPES,
+                CodegenConstants.NULLABLE_REFERENCE_TYPES_DESC,
+                this.nullReferenceTypesFlag);
+
         addSwitch(CodegenConstants.HIDE_GENERATION_TIMESTAMP,
                 CodegenConstants.HIDE_GENERATION_TIMESTAMP_DESC,
                 this.hideGenerationTimestamp);
diff --git a/modules/openapi-generator/src/main/resources/csharp-netcore/netcore_project.mustache b/modules/openapi-generator/src/main/resources/csharp-netcore/netcore_project.mustache
index 7d77d34b4d8..4f29dcf3d34 100644
--- a/modules/openapi-generator/src/main/resources/csharp-netcore/netcore_project.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp-netcore/netcore_project.mustache
@@ -19,6 +19,9 @@
     <RepositoryType>git</RepositoryType>{{#releaseNote}}
     <PackageReleaseNotes>{{releaseNote}}</PackageReleaseNotes>{{/releaseNote}}{{#packageTags}}
     <PackageTags>{{{packageTags}}}</PackageTags>{{/packageTags}}
+    {{#nullableReferenceTypes}}
+    <Nullable>annotations</Nullable>
+    {{/nullableReferenceTypes}}
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/modules/openapi-generator/src/main/resources/csharp/netcore_project.mustache b/modules/openapi-generator/src/main/resources/csharp/netcore_project.mustache
index 2cb30d650a5..fd4168d0d4c 100644
--- a/modules/openapi-generator/src/main/resources/csharp/netcore_project.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp/netcore_project.mustache
@@ -15,6 +15,9 @@
     <GenerateBindingRedirectsOutputType>true</GenerateBindingRedirectsOutputType>
     <RootNamespace>{{packageName}}</RootNamespace>
     <Version>{{packageVersion}}</Version>
+    {{#nullableReferenceTypes}}
+    <Nullable>annotations</Nullable>
+    {{/nullableReferenceTypes}}
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/csharp/CSharpModelTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/csharp/CSharpModelTest.java
index 4a8f8f3e3bc..b387a0a2986 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/csharp/CSharpModelTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/csharp/CSharpModelTest.java
@@ -21,6 +21,7 @@ import com.google.common.collect.Sets;
 import io.swagger.v3.oas.models.OpenAPI;
 import io.swagger.v3.oas.models.media.*;
 import io.swagger.v3.parser.util.SchemaTypeUtil;
+import org.openapitools.codegen.CodegenConstants;
 import org.openapitools.codegen.CodegenModel;
 import org.openapitools.codegen.CodegenProperty;
 import org.openapitools.codegen.DefaultCodegen;
@@ -335,7 +336,7 @@ public class CSharpModelTest {
                 .addProperties("subObject",  new Schema().addProperties("name", new StringSchema()).nullable(true))
                 .addRequiredItem("id");
         final DefaultCodegen codegen = new AspNetCoreServerCodegen();
-        codegen.additionalProperties().put(AspNetCoreServerCodegen.NULLABLE_REFERENCE_TYPES, true);
+        codegen.additionalProperties().put(CodegenConstants.NULLABLE_REFERENCE_TYPES, true);
         codegen.processOpts();
         OpenAPI openAPI = TestUtils.createOpenAPIWithOneSchema("sample", model);
         codegen.setOpenAPI(openAPI);