diff --git a/project/config/cfgdefs.sh b/project/config/cfgdefs.sh
index a8648ca..2ff7631 100644
--- a/project/config/cfgdefs.sh
+++ b/project/config/cfgdefs.sh
@@ -44,6 +44,7 @@ cfgdefs_bootstrap()
 	cfgdefs_cflags="$cfgdefs_cflags -I${mb_source_dir}/src/internal"
 	cfgdefs_cflags="$cfgdefs_cflags -D_PATH_DEFSYSPATH=\"${mb_source_dir}/mk\""
 	cfgdefs_cflags="$cfgdefs_cflags $cfgdefs_added_defs"
+	cfgdefs_cflags="$cfgdefs_cflags -D_XOPEN_SOURCE=700"
 
 	cfgtest_native_section