Error: function wgdb.to_string is not accessible from module wgdb

[Charles Hixson]

What does the following error mean?
wgdb.d(24): Error: function wgdb.to_string is not accessible from module 
wgdb

The function in question is the pretty simple:
package	string to_string(const char *zString)
{	int i;
	for (i = 0; zString[i] != 0; ++i) {};
	return to!string(zString[0..i]);
}

It's a function at the top level.  If I remove "package" the compiler 
error disappears.  But because of it's peculiar name, I wanted to 
restrict visibility.  If it matters, the file has no module statement.