diff --git a/mk/os-Linux.mk b/mk/os-Linux.mk
index 2479ff5b..9e8a1485 100644
--- a/mk/os-Linux.mk
+++ b/mk/os-Linux.mk
@@ -11,7 +11,7 @@
 SFX=		.Linux.in
 PKG_PREFIX?=	/usr
 
-CPPFLAGS+=	-D_DEFAULT_SOURCE
+CPPFLAGS+=	-D_DEFAULT_SOURCE -D_POSIX_C_SOURCE=200809L
 LIBDL=		-Wl,-Bdynamic -ldl
 
 ifeq (${MKSELINUX},yes)