DLLs, callbacks, and the GC that loves them

I have a question about how GC works in DLLs with callbacks. Let's say I have a BlitzMax-written DLL and a C/C++-written main program calling the DLL. I pass a C function to the DLL as a callback to use during a certain task. The main program looks like this:

int callback {
Return 1;
}

MyFunction(callback);

The DLL looks like this:

Function MyFunction( callback:Int() ) "win32"
GCEnter()
'GC-What goes here?
callback()
'GC-What goes here?
EndFunction

Is there something I need to do with the GC when the callback gets used? Like GCSuspend/Resume, or GCLeave/Enter? What is the correct way of handling this? Thanks.