diff --git a/Lib/csharp/std_wstring.i b/Lib/csharp/std_wstring.i
index 09bdaaaa2..b18a2cca4 100644
--- a/Lib/csharp/std_wstring.i
+++ b/Lib/csharp/std_wstring.i
@@ -23,7 +23,10 @@ class wstring;
 
 // wstring
 %typemap(ctype, out="void *") wstring "wchar_t *"
-%typemap(imtype, inattributes="[global::System.Runtime.InteropServices.MarshalAs(global::System.Runtime.InteropServices.UnmanagedType.LPWStr)]") wstring "string"
+%typemap(imtype,
+         inattributes="[global::System.Runtime.InteropServices.MarshalAs(global::System.Runtime.InteropServices.UnmanagedType.LPWStr)]",
+         outattributes="[return: global::System.Runtime.InteropServices.MarshalAs(global::System.Runtime.InteropServices.UnmanagedType.LPWStr)]"
+         ) wstring "string"
 %typemap(cstype) wstring "string"
 %typemap(csdirectorin) wstring "$iminput"
 %typemap(csdirectorout) wstring "$cscall"
diff --git a/Lib/csharp/wchar.i b/Lib/csharp/wchar.i
index 9361edf6f..79fb5a8cf 100644
--- a/Lib/csharp/wchar.i
+++ b/Lib/csharp/wchar.i
@@ -20,6 +20,7 @@ static SWIG_CSharpWStringHelperCallback SWIG_csharp_wstring_callback = NULL;
 %pragma(csharp) imclasscode=%{
   protected class SWIGWStringHelper {
 
+    [return: global::System.Runtime.InteropServices.MarshalAs(global::System.Runtime.InteropServices.UnmanagedType.LPWStr)]
     public delegate string SWIGWStringDelegate(global::System.IntPtr message);
     static SWIGWStringDelegate wstringDelegate = new SWIGWStringDelegate(CreateWString);