diff --git a/arch/sandbox/cpu/Makefile b/arch/sandbox/cpu/Makefile
index 404ff67..58c2537 100644
--- a/arch/sandbox/cpu/Makefile
+++ b/arch/sandbox/cpu/Makefile
@@ -10,5 +10,7 @@
 obj-y	:= cpu.o os.o start.o state.o
 
 # os.c is build in the system environment, so needs standard includes
-$(obj)os.o: ALL_CFLAGS := $(filter-out -nostdinc,$(ALL_CFLAGS))
-$(obj).depend.os: CPPFLAGS := $(filter-out -nostdinc,$(CPPFLAGS))
+$(obj)os.o: ALL_CFLAGS := $(BASE_CPPFLAGS) \
+	$(patsubst %, -idirafter %, $(BASE_INCLUDE_DIRS))
+$(obj).depend.os: CPPFLAGS := $(BASE_CPPFLAGS) \
+	$(patsubst %, -idirafter %, $(BASE_INCLUDE_DIRS))
diff --git a/config.mk b/config.mk
index 206de20..d5b09a0 100644
--- a/config.mk
+++ b/config.mk
@@ -250,11 +250,16 @@
 endif
 endif
 
+# Sandbox needs the base flags and includes, so keep them around
+BASE_CPPFLAGS := $(CPPFLAGS)
+
 ifneq ($(OBJTREE),$(SRCTREE))
-CPPFLAGS += -I$(OBJTREE)/include
+BASE_INCLUDE_DIRS := $(OBJTREE)/include
 endif
 
-CPPFLAGS += -I$(TOPDIR)/include -I$(SRCTREE)/arch/$(ARCH)/include
+BASE_INCLUDE_DIRS += $(TOPDIR)/include $(SRCTREE)/arch/$(ARCH)/include
+
+CPPFLAGS += $(patsubst %, -I%, $(BASE_INCLUDE_DIRS))
 CPPFLAGS += -fno-builtin -ffreestanding -nostdinc	\
 	-isystem $(gccincdir) -pipe $(PLATFORM_CPPFLAGS)