--- src/support/lyxsum.cpp.orig	2008-01-12 18:10:41.000000000 +0100
+++ src/support/lyxsum.cpp	2008-01-12 18:11:17.000000000 +0100
@@ -41,6 +41,7 @@ template struct boost::detail::crc_table
 
 // Make sure we get modern version of mmap and friends with void*,
 // not `compatibility' version with caddr_t.
+#undef _POSIX_C_SOURCE
 #define _POSIX_C_SOURCE 199506L
 
 #ifdef HAVE_SYS_TYPES_H