diff --git a/src/SoapCore/SoapEndpointMiddleware.cs b/src/SoapCore/SoapEndpointMiddleware.cs
index 13739531..bb8d8bdd 100644
--- a/src/SoapCore/SoapEndpointMiddleware.cs
+++ b/src/SoapCore/SoapEndpointMiddleware.cs
@@ -1146,14 +1146,14 @@ private async Task ProcessMetaFromFile(HttpContext httpContext, bool showDocumen
 				meta.CurrentWebService = mapping.UrlOverride;
 			}
 
-			meta.WSDLFolder = mapping.WSDLFolder;
+			meta.WSDLFolder = mapping.WSDLFolder ?? "";
 			meta.XsdFolder = mapping.SchemaFolder;
 			meta.ServerUrl = GetServerUrl(options, httpContext);
 
 			string wsdlfile = mapping.WsdlFile;
 
-			string path = options.AppPath;
-			string wsdl = await meta.ReadLocalFileAsync(path + Path.AltDirectorySeparatorChar + meta.WSDLFolder + Path.AltDirectorySeparatorChar + wsdlfile);
+			string path = options.AppPath ?? "";
+			string wsdl = await meta.ReadLocalFileAsync(Path.Combine(path, meta.WSDLFolder, wsdlfile));
 			string modifiedWsdl = meta.ModifyWSDLAddRightSchemaPath(wsdl);
 
 			if (showDocumentation)