diff --git a/modules/openapi-generator/src/main/resources/csharp/api.mustache b/modules/openapi-generator/src/main/resources/csharp/api.mustache
index 85aa372e54f..3ea861f24ce 100644
--- a/modules/openapi-generator/src/main/resources/csharp/api.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp/api.mustache
@@ -308,12 +308,12 @@ namespace {{packageName}}.{{apiPackage}}
 
             {{#returnType}}
             return new ApiResponse<{{{returnType}}}>(localVarStatusCode,
-                localVarResponse.Headers.ToDictionary(x => x.{{^netStandard}}Name{{/netStandard}}{{#netStandard}}Key{{/netStandard}}, x => x.Value.ToString()),
+                localVarResponse.Headers.ToDictionary(x => x.{{^netStandard}}Name{{/netStandard}}{{#netStandard}}Key{{/netStandard}}, x => string.Join(",", x.Value)),
                 ({{{returnType}}}) this.Configuration.ApiClient.Deserialize(localVarResponse, typeof({{#returnContainer}}{{{returnContainer}}}{{/returnContainer}}{{^returnContainer}}{{{returnType}}}{{/returnContainer}})));
             {{/returnType}}
             {{^returnType}}
             return new ApiResponse<Object>(localVarStatusCode,
-                localVarResponse.Headers.ToDictionary(x => x.{{^netStandard}}Name{{/netStandard}}{{#netStandard}}Key{{/netStandard}}, x => x.Value.ToString()),
+                localVarResponse.Headers.ToDictionary(x => x.{{^netStandard}}Name{{/netStandard}}{{#netStandard}}Key{{/netStandard}}, x => string.Join(",", x.Value)),
                 null);
             {{/returnType}}
         }
@@ -444,12 +444,12 @@ namespace {{packageName}}.{{apiPackage}}
 
             {{#returnType}}
             return new ApiResponse<{{{returnType}}}>(localVarStatusCode,
-                localVarResponse.Headers.ToDictionary(x => x.{{^netStandard}}Name{{/netStandard}}{{#netStandard}}Key{{/netStandard}}, x => x.Value.ToString()),
+                localVarResponse.Headers.ToDictionary(x => x.{{^netStandard}}Name{{/netStandard}}{{#netStandard}}Key{{/netStandard}}, x => string.Join(",", x.Value)),
                 ({{{returnType}}}) this.Configuration.ApiClient.Deserialize(localVarResponse, typeof({{#returnContainer}}{{{returnContainer}}}{{/returnContainer}}{{^returnContainer}}{{{returnType}}}{{/returnContainer}})));
             {{/returnType}}
             {{^returnType}}
             return new ApiResponse<Object>(localVarStatusCode,
-                localVarResponse.Headers.ToDictionary(x => x.{{^netStandard}}Name{{/netStandard}}{{#netStandard}}Key{{/netStandard}}, x => x.Value.ToString()),
+                localVarResponse.Headers.ToDictionary(x => x.{{^netStandard}}Name{{/netStandard}}{{#netStandard}}Key{{/netStandard}}, x => string.Join(",", x.Value)),
                 null);
             {{/returnType}}
         }