diff --git a/BaseTools/Source/C/Makefiles/header.makefile b/BaseTools/Source/C/Makefiles/header.makefile
index 3049587797..54d3c78f97 100644
--- a/BaseTools/Source/C/Makefiles/header.makefile
+++ b/BaseTools/Source/C/Makefiles/header.makefile
@@ -41,7 +41,12 @@ endif
 
 INCLUDE = $(TOOL_INCLUDE) -I $(MAKEROOT) -I $(MAKEROOT)/Include/Common -I $(MAKEROOT)/Include/ -I $(MAKEROOT)/Include/IndustryStandard -I $(MAKEROOT)/Common/ -I .. -I . $(ARCH_INCLUDE) 
 CPPFLAGS = $(INCLUDE)
+ifeq ($(DARWIN),Darwin)
+# assume clang or clang compatible flags on OS X
 CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -Wall -Werror -Wno-deprecated-declarations -Wno-self-assign -nostdlib -c -g
+else
+CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -Wall -Werror -Wno-deprecated-declarations -nostdlib -c -g
+endif
 LFLAGS =
 
 ifeq ($(ARCH), IA32)
@@ -50,8 +55,7 @@ ifeq ($(ARCH), IA32)
 #  to x86_64. So make sure tools match uname -m. You can manual have a 64-bit kernal on Snow Leopard
 #  so only do this is uname -m returns i386.
 #
-uname_s = $(shell uname -s)
-ifeq ($(uname_s),Darwin)
+ifeq ($(DARWIN),Darwin)
   CFLAGS   += -arch i386
   CPPFLAGS += -arch i386
   LFLAGS   += -arch i386