C++ struct alignment question

I have a predefined struct (actually several) where variables span across 32-bit word boundary. In Linux (and Windows using GCC) I am able to get my structs to pack to the correct size using 'attribute((packed))'. However I cannot get it to work the same way using VC++ and #pragma pack.

Using GCC this returns a correct size of 6 bytes:

struct
{
    unsigned int   a                : 3;
    unsigned int   b                : 1;
    unsigned int   c                : 15;
    unsigned int   troubleMaker     : 16;
    unsigned short padding          : 13;
} __attribute__((packed)) s;

Using VC++ this returns an incorrect size of 8 bytes

#pragma pack(push)
#pragma pack(1)

struct
{
    unsigned int   a                : 3;
    unsigned int   b                : 1;
    unsigned int   c                : 15;
    unsigned int   troubleMaker     : 16;
    unsigned short padding          : 13;
} s;

#pragma pack(pop)

I can get things to work by splitting 'troubleMaker' across the boundary manually but I'd prefer not to. Any ideas?