diff -Nurp VirtualBox-5.1.0.p20/Config.kmk VirtualBox-5.1.0.p21/Config.kmk
--- VirtualBox-5.1.0.p20/Config.kmk	2016-07-12 17:47:20.000000000 +0300
+++ VirtualBox-5.1.0.p21/Config.kmk	2016-07-13 19:37:01.512721807 +0300
@@ -3446,19 +3446,19 @@ VBOXLNX32GUEST_SUFF_LIB = .a
 # SDKs for external libraries.
 #
 SDK_VBOX_LIBXML2          = .
-SDK_VBOX_LIBXML2_INCS   ?= $(PATH_ROOT)/src/libs/libxml2-2.9.2/include
+SDK_VBOX_LIBXML2_INCS   ?= /usr/include/libxml2
 SDK_VBOX_LIBXML2_DEFS  ?= _REENTRANT
 SDK_VBOX_LIBXML2_DEFS.win += WIN32 _WINDOWS _MBCS
 # note: no linking to LIB here, we do that explicitly in src/VBox/Runtime/Makefile.kmk to link
 # libxml against VBoxRT
 
 SDK_VBOX_LIBPNG       = .
-SDK_VBOX_LIBPNG_INCS ?= $(PATH_ROOT)/src/libs/libpng-1.2.54
+SDK_VBOX_LIBPNG_INCS ?= `/usr/bin/pkg-config libpng --variable=includedir`
 SDK_VBOX_LIBPNG_LIBS ?= $(PATH_STAGE_LIB)/VBox-libpng$(VBOX_SUFF_LIB)
 
 SDK_VBOX_ZLIB         = .
 if1of ($(KBUILD_TARGET), os2 solaris win)
- SDK_VBOX_ZLIB_INCS  ?= $(PATH_ROOT)/src/libs/zlib-1.2.8
+ SDK_VBOX_ZLIB_INCS  ?= /usr/include/
  SDK_VBOX_ZLIB_LIBS  ?= $(PATH_STAGE_LIB)/VBox-zlib$(VBOX_SUFF_LIB)
 else
  SDK_VBOX_ZLIB_INCS  ?=