Expat on 64 bit Linux

Hi,
I'm trying to use expat (the last version) on a 64 bit Linux (Intel).  
Both XML_UNICODE_WCHAR_T and XML_UNICODE are defined, and  
sizeof(wchar_t) == sizeof(XML_Char) == 4 bytes
I understand that when my callbacks get called, each XML_Char should  
hold one character (at least that is the way it is working on a 32 bit  
Windows).
Instead of that, what I'm getting is 2 characters in each XML_Char  
element. Like if it was treating a 4 byte XML_Char array as a 2 byte  
XML_Char array.
Can anyone help me with this ?
Thanks in advance.