--- VirtualBox-1.5.6_OSE/Config.kmk
+++ VirtualBox-1.5.6_OSE/Config.kmk
@@ -1225,7 +1225,14 @@
     kernelpath := $(realpath $(VBOX_LINUX_SRC)/$(kernelsrc))
     VBOX_LINUX_INCS                 += $(VBOX_LINUX_SRC)/include2 $(kernelpath)/include
    else
-    kernelpath := $(VBOX_LINUX_SRC)
+    # 2.6.25 format for splitted sources
+    kernelsrc := $(shell $(SED_EXT) -ne 's+^MAKEARGS := -C++p' $(VBOX_LINUX_SRC)/Makefile)
+    ifneq ($(kernelsrc),)
+     kernelpath := $(realpath $(VBOX_LINUX_SRC)/$(kernelsrc))
+     VBOX_LINUX_INCS                 += $(VBOX_LINUX_SRC)/include2 $(kernelpath)/include
+    else
+     kernelpath := $(VBOX_LINUX_SRC)
+    endif
    endif
    ifeq ($(BUILD_TARGET_ARCH),x86)
      VBOX_LINUX_INCS                += $(kernelpath)/include/asm-i386/mach-default \
--- VirtualBox-1.5.6_OSE/src/VBox/Runtime/Makefile.kmk
+++ VirtualBox-1.5.6_OSE/src/VBox/Runtime/Makefile.kmk
@@ -58,6 +58,7 @@
 
 # global (for now at least)
 INCS += include
+INCS += /usr/include
 
 ifneq ($(wildcard ./kLdr/kLdrModMachO.c),)
  ifeq ($(filter-out darwin win os2,$(BUILD_TARGET)),)
