diff --git a/clang/lib/Headers/cpuid.h b/clang/lib/Headers/cpuid.h
--- a/clang/lib/Headers/cpuid.h
+++ b/clang/lib/Headers/cpuid.h
@@ -7,6 +7,9 @@
  *===-----------------------------------------------------------------------===
  */
 
+#ifndef __CPUID_H
+#define __CPUID_H
+
 #if !(__x86_64__ || __i386__)
 #error this header is for x86 only
 #endif
@@ -312,3 +315,5 @@
     __cpuid_count(__leaf, __subleaf, *__eax, *__ebx, *__ecx, *__edx);
     return 1;
 }
+
+#endif /* __CPUID_H */
diff --git a/clang/test/Headers/cpuid.c b/clang/test/Headers/cpuid.c
--- a/clang/test/Headers/cpuid.c
+++ b/clang/test/Headers/cpuid.c
@@ -2,6 +2,7 @@
 // RUN: %clang_cc1 %s -ffreestanding -triple i386 -emit-llvm -o - | FileCheck %s --check-prefix=CHECK-32
 
 #include <cpuid.h>
+#include <cpuid.h> // Make sure multiple inclusion protection works.
 
 // CHECK-64: {{.*}} call { i32, i32, i32, i32 } asm "  xchgq  %rbx,${1:q}\0A cpuid\0A xchgq %rbx,${1:q}", "={ax},=r,={cx},={dx},0,~{dirflag},~{fpsr},~{flags}"(i32 %{{[a-z0-9]+}})
 // CHECK-64: {{.*}} call { i32, i32, i32, i32 } asm "  xchgq  %rbx,${1:q}\0A  cpuid\0A  xchgq  %rbx,${1:q}", "={ax},=r,={cx},={dx},0,2,~{dirflag},~{fpsr},~{flags}"(i32 %{{[a-z0-9]+}}, i32 %{{[a-z0-9]+}})