diff --git a/modules/openapi-generator/src/main/resources/csharp/api.mustache b/modules/openapi-generator/src/main/resources/csharp/api.mustache
index 2a6bf3cf4952..f040c439025d 100644
--- a/modules/openapi-generator/src/main/resources/csharp/api.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp/api.mustache
@@ -384,7 +384,7 @@ namespace {{packageName}}.{{apiPackage}}
             if ({{paramName}} != null) localVarHeaderParams.Add("{{baseName}}", this.Configuration.ApiClient.ParameterToString({{paramName}})); // header parameter
             {{/headerParams}}
             {{#formParams}}
-            if ({{paramName}} != null) {{#isFile}}localVarFileParams.Add("{{baseName}}", this.Configuration.ApiClient.ParameterToFile("{{baseName}}", {{paramName}}));{{/isFile}}{{^isFile}}localVarFormParams.Add("{{baseName}}", this.Configuration.ApiClient.ParameterToString({{paramName}})); // form parameter{{/isFile}}
+            if ({{paramName}} != null) {{#isFile}}localVarFileParams.Add("{{baseName}}", this.Configuration.ApiClient.ParameterToFile("{{baseName}}", {{paramName}}));{{/isFile}}{{^isFile}}localVarFormParams.Add("{{baseName}}", this.Configuration.ApiClient.{{#isPrimitiveType}}ParameterToString{{/isPrimitiveType}}{{^isPrimitiveType}}Serialize{{/isPrimitiveType}}({{paramName}})); // form parameter{{/isFile}}
             {{/formParams}}
             {{#bodyParam}}
             if ({{paramName}} != null && {{paramName}}.GetType() != typeof(byte[]))
diff --git a/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Api/FakeApi.cs
index 0defcc20a751..e7f144292bb9 100644
--- a/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2403,7 +2403,7 @@ public async System.Threading.Tasks.Task<ApiResponse<ModelClient>> TestClientMod
             if (enumQueryDouble != null) localVarQueryParams.AddRange(this.Configuration.ApiClient.ParameterToKeyValuePairs("", "enum_query_double", enumQueryDouble)); // query parameter
             if (enumHeaderStringArray != null) localVarHeaderParams.Add("enum_header_string_array", this.Configuration.ApiClient.ParameterToString(enumHeaderStringArray)); // header parameter
             if (enumHeaderString != null) localVarHeaderParams.Add("enum_header_string", this.Configuration.ApiClient.ParameterToString(enumHeaderString)); // header parameter
-            if (enumFormStringArray != null) localVarFormParams.Add("enum_form_string_array", this.Configuration.ApiClient.ParameterToString(enumFormStringArray)); // form parameter
+            if (enumFormStringArray != null) localVarFormParams.Add("enum_form_string_array", this.Configuration.ApiClient.Serialize(enumFormStringArray)); // form parameter
             if (enumFormString != null) localVarFormParams.Add("enum_form_string", this.Configuration.ApiClient.ParameterToString(enumFormString)); // form parameter
 
 
diff --git a/samples/client/petstore/csharp/OpenAPIClientNetStandard/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClientNetStandard/src/Org.OpenAPITools/Api/FakeApi.cs
index 51077f789e20..129610f908f9 100644
--- a/samples/client/petstore/csharp/OpenAPIClientNetStandard/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClientNetStandard/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2403,7 +2403,7 @@ public async System.Threading.Tasks.Task<ApiResponse<ModelClient>> TestClientMod
             if (enumQueryDouble != null) localVarQueryParams.AddRange(this.Configuration.ApiClient.ParameterToKeyValuePairs("", "enum_query_double", enumQueryDouble)); // query parameter
             if (enumHeaderStringArray != null) localVarHeaderParams.Add("enum_header_string_array", this.Configuration.ApiClient.ParameterToString(enumHeaderStringArray)); // header parameter
             if (enumHeaderString != null) localVarHeaderParams.Add("enum_header_string", this.Configuration.ApiClient.ParameterToString(enumHeaderString)); // header parameter
-            if (enumFormStringArray != null) localVarFormParams.Add("enum_form_string_array", this.Configuration.ApiClient.ParameterToString(enumFormStringArray)); // form parameter
+            if (enumFormStringArray != null) localVarFormParams.Add("enum_form_string_array", this.Configuration.ApiClient.Serialize(enumFormStringArray)); // form parameter
             if (enumFormString != null) localVarFormParams.Add("enum_form_string", this.Configuration.ApiClient.ParameterToString(enumFormString)); // form parameter
 
 
diff --git a/samples/client/petstore/csharp/OpenAPIClientWithPropertyChanged/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClientWithPropertyChanged/src/Org.OpenAPITools/Api/FakeApi.cs
index 0defcc20a751..e7f144292bb9 100644
--- a/samples/client/petstore/csharp/OpenAPIClientWithPropertyChanged/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClientWithPropertyChanged/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2403,7 +2403,7 @@ public async System.Threading.Tasks.Task<ApiResponse<ModelClient>> TestClientMod
             if (enumQueryDouble != null) localVarQueryParams.AddRange(this.Configuration.ApiClient.ParameterToKeyValuePairs("", "enum_query_double", enumQueryDouble)); // query parameter
             if (enumHeaderStringArray != null) localVarHeaderParams.Add("enum_header_string_array", this.Configuration.ApiClient.ParameterToString(enumHeaderStringArray)); // header parameter
             if (enumHeaderString != null) localVarHeaderParams.Add("enum_header_string", this.Configuration.ApiClient.ParameterToString(enumHeaderString)); // header parameter
-            if (enumFormStringArray != null) localVarFormParams.Add("enum_form_string_array", this.Configuration.ApiClient.ParameterToString(enumFormStringArray)); // form parameter
+            if (enumFormStringArray != null) localVarFormParams.Add("enum_form_string_array", this.Configuration.ApiClient.Serialize(enumFormStringArray)); // form parameter
             if (enumFormString != null) localVarFormParams.Add("enum_form_string", this.Configuration.ApiClient.ParameterToString(enumFormString)); // form parameter