Gendarme warning about no marshaling information for boolean parameter (P/Invoke)

Greetings everyone!

Consider the following code:

uses
  System.Runtime.InteropServices,
  System.Security;

type
  [SuppressUnmanagedCodeSecurity]
  UnsafeNativeMethods = static assembly class
  public
    [DllImport('kernel32.dll', SetLastError := true)]
    class method FreeLibrary(hModule: IntPtr): [MarshalAs(UnmanagedType.Bool)] Boolean; external;
  end;

If I add it to the interface section of the program.pas file in a new .NET 4 or 4.5 console application, enable Gendarme code analysis and build the solution, I get the following warning:

Program.pas(14,5): warning High/Normal: No marshaling information is supplied for boolean parameters(s) on this p/invoke declaration. Specify, even if just for clarity, the size of the unmanaged boolean representation.

As you can see from the code, I have tried to specify how the return type should be marshalled. Is there any other way I should write this?

Oxygene version 5.2.39.1091