diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -146,7 +146,8 @@
   ``[[clang::guard(nocf)]]``, which is equivalent to ``__declspec(guard(nocf))``
   when using the MSVC environment. This is to support enabling Windows Control
   Flow Guard checks with the ability to disable them for specific functions when
-  using the MinGW environment.
+  using the MinGW environment. This attribute is only available for Windows
+  targets.
 
 Windows Support
 ---------------
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -399,6 +399,9 @@
 def TargetX86 : TargetArch<["x86"]>;
 def TargetAnyX86 : TargetArch<["x86", "x86_64"]>;
 def TargetWebAssembly : TargetArch<["wasm32", "wasm64"]>;
+def TargetWindows : TargetSpec {
+  let OSes = ["Win32"];
+}
 def TargetHasDLLImportExport : TargetSpec {
   let CustomCode = [{ Target.getTriple().hasDLLImportExport() }];
 }
@@ -3494,7 +3497,7 @@
   let Documentation = [MSAllocatorDocs];
 }
 
-def CFGuard : InheritableAttr {
+def CFGuard : InheritableAttr, TargetSpecificAttr<TargetWindows> {
   // Currently only the __declspec(guard(nocf)) modifier is supported. In future
   // we might also want to support __declspec(guard(suppress)).
   let Spellings = [Declspec<"guard">, Clang<"guard">];
diff --git a/clang/test/Sema/attr-guard_nocf.c b/clang/test/Sema/attr-guard_nocf.c
--- a/clang/test/Sema/attr-guard_nocf.c
+++ b/clang/test/Sema/attr-guard_nocf.c
@@ -2,10 +2,14 @@
 // RUN: %clang_cc1 -triple %ms_abi_triple -fms-extensions -verify -std=c++11 -fsyntax-only -x c++ %s
 // RUN: %clang_cc1 -triple x86_64-w64-windows-gnu -verify -fsyntax-only %s
 // RUN: %clang_cc1 -triple x86_64-w64-windows-gnu -verify -std=c++11 -fsyntax-only -x c++ %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -verify -fsyntax-only %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -verify -std=c++11 -fsyntax-only -x c++ %s
 
 // The x86_64-w64-windows-gnu version tests mingw target, which relies on
 // __declspec(...) being defined as __attribute__((...)) by compiler built-in.
 
+#if defined(_WIN32)
+
 // Function definition.
 __declspec(guard(nocf)) void testGuardNoCF(void) { // no warning
 }
@@ -35,3 +39,9 @@
 // 'guard' Attribute argument must be a supported identifier.
 __declspec(guard(cf)) void testGuardNoCFInvalidParam(void) { // expected-warning {{'guard' attribute argument not supported: 'cf'}}
 }
+
+#else
+
+__attribute((guard(nocf))) void testGNUStyleGuardNoCF(void) {} // expected-warning {{unknown attribute 'guard' ignored}}
+
+#endif