diff --git a/mk/os-GNU-kFreeBSD.mk b/mk/os-GNU-kFreeBSD.mk
index 4fc934e0..93b48291 100644
--- a/mk/os-GNU-kFreeBSD.mk
+++ b/mk/os-GNU-kFreeBSD.mk
@@ -13,6 +13,6 @@
 SFX=		.GNU-kFreeBSD.in
 PKG_PREFIX?=	/usr
 
-CPPFLAGS+=	-D_BSD_SOURCE -D_XOPEN_SOURCE=700
+CPPFLAGS+=	-D_BSD_SOURCE
 LIBDL=		-Wl,-Bdynamic -ldl
 LIBKVM?=
diff --git a/mk/os-GNU.mk b/mk/os-GNU.mk
index d5c4172f..adaefd44 100644
--- a/mk/os-GNU.mk
+++ b/mk/os-GNU.mk
@@ -11,5 +11,5 @@
 SFX=		.GNU.in
 PKG_PREFIX?=	/usr
 
-CPPFLAGS+=	-D_DEFAULT_SOURCE -D_XOPEN_SOURCE=700 -DMAXPATHLEN=4096 -DPATH_MAX=4096
+CPPFLAGS+=	-D_DEFAULT_SOURCE -DMAXPATHLEN=4096 -DPATH_MAX=4096
 LIBDL=		-Wl,-Bdynamic -ldl
diff --git a/mk/os-Linux.mk b/mk/os-Linux.mk
index 3a3c5167..2479ff5b 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 -D_XOPEN_SOURCE=700
+CPPFLAGS+=	-D_DEFAULT_SOURCE
 LIBDL=		-Wl,-Bdynamic -ldl
 
 ifeq (${MKSELINUX},yes)