Index: VirtualBox-5.1.26/src/VBox/Additions/x11/vboxvideo/Makefile.kmk
===================================================================
--- VirtualBox-5.1.26.orig/src/VBox/Additions/x11/vboxvideo/Makefile.kmk
+++ VirtualBox-5.1.26/src/VBox/Additions/x11/vboxvideo/Makefile.kmk
@@ -23,6 +23,9 @@ vboxvideo_70_DEFS := \
 ifeq ($(KBUILD_TARGET),solaris) # don't use .solaris or anything here.
  vboxvideo_70_DEFS += __EXTENSIONS__  ## @todo Why this?
 endif
+if1of ($(KBUILD_TARGET), linux)
+ vboxvideo_70_DEFS += _POSIX_SOURCE ## X requires POSIX extensions
+endif
 vboxvideo_13_DEFS := $(vboxvideo_70_DEFS) VBOXVIDEO_13
 vboxvideo_15_DEFS := \
 	$(vboxvideo_13_DEFS) NO_ANSIC PCIACCESS XSERVER_LIBPCIACCESS _XORG_SERVER_H_ _DIX_CONFIG_H_
Index: VirtualBox-5.1.26/src/VBox/Additions/x11/vboxvideo/edid.c
===================================================================
--- VirtualBox-5.1.26.orig/src/VBox/Additions/x11/vboxvideo/edid.c
+++ VirtualBox-5.1.26/src/VBox/Additions/x11/vboxvideo/edid.c
@@ -44,10 +44,6 @@
  *    Dave Airlie <airlied@redhat.com>
  */
 
-#if XORG_VERSION_CURRENT >= 11900000
-#include <bits/sigset.h>
-typedef __sigset_t sigset_t;
-#endif
 #include <misc.h>
 #include <xf86DDC.h>
 #include <xf86Crtc.h>
Index: VirtualBox-5.1.26/src/VBox/Additions/x11/vboxvideo/pointer.c
===================================================================
--- VirtualBox-5.1.26.orig/src/VBox/Additions/x11/vboxvideo/pointer.c
+++ VirtualBox-5.1.26/src/VBox/Additions/x11/vboxvideo/pointer.c
@@ -15,10 +15,6 @@
  * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
  */
 
-#if XORG_VERSION_CURRENT >= 11900000
-#include <bits/sigset.h>
-typedef __sigset_t sigset_t;
-#endif
 #include <VBox/VBoxGuestLib.h>
 
 #ifndef PCIACCESS
Index: VirtualBox-5.1.26/src/VBox/Additions/x11/vboxvideo/vboxvideo.h
===================================================================
--- VirtualBox-5.1.26.orig/src/VBox/Additions/x11/vboxvideo/vboxvideo.h
+++ VirtualBox-5.1.26/src/VBox/Additions/x11/vboxvideo/vboxvideo.h
@@ -52,10 +52,6 @@
 #ifndef _VBOXVIDEO_H_
 #define _VBOXVIDEO_H_
 
-#if XORG_VERSION_CURRENT >= 11900000
-#include <bits/sigset.h>
-typedef __sigset_t sigset_t;
-#endif
 #include <VBox/VBoxVideoGuest.h>
 #include <VBox/VBoxVideo.h>
 #include "version-generated.h"
Index: VirtualBox-5.1.26/src/VBox/ExtPacks/VBoxDTrace/Makefile.kmk
===================================================================
--- VirtualBox-5.1.26.orig/src/VBox/ExtPacks/VBoxDTrace/Makefile.kmk
+++ VirtualBox-5.1.26/src/VBox/ExtPacks/VBoxDTrace/Makefile.kmk
@@ -103,7 +103,7 @@ if defined(VBOX_WITH_EXTPACK_VBOXDTRACE)
  VBoxDTraceCmd_TEMPLATE = VBoxR3ExtPackDTrace
  VBoxDTraceCmd_DEFS = RTMEM_WRAP_TO_EF_APIS VBOX_EXTPACK_VBOXDTRACE_MANGLED_NAME=\"$(VBOX_EXTPACK_VBOXDTRACE_MANGLED_NAME)\"
  #VBoxDTraceCmd_DEFS += YYDEBUG
- VBoxDTraceCmd_DEFS.linux = _XOPEN_SOURCE=700
+ VBoxDTraceCmd_DEFS.linux = _XOPEN_SOURCE=700 _DEFAULT_SOURCE
  VBoxDTraceCmd_DEFS.win = YY_USE_PROTOS=1 YYENABLE_NLS=0 YYLTYPE_IS_TRIVIAL=0
  VBoxDTraceCmd_SDKS = VBOX_ZLIB
  ifn1of ($(KBUILD_TARGET), win)