Index: clang/include/clang/Basic/DiagnosticParseKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticParseKinds.td
+++ clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -126,7 +126,7 @@
 def note_previous_default_assoc : Note<
   "previous default generic association is here">;
 
-def ext_c11_alignment : Extension<
+def ext_c11_feature : Extension<
   "%0 is a C11-specific feature">, InGroup<C11>;
 
 def ext_c11_noreturn : Extension<
Index: clang/lib/Parse/ParseDecl.cpp
===================================================================
--- clang/lib/Parse/ParseDecl.cpp
+++ clang/lib/Parse/ParseDecl.cpp
@@ -3566,6 +3566,8 @@
       isStorageClass = true;
       break;
     case tok::kw__Thread_local:
+      if (!getLangOpts().C11)
+        Diag(Tok, diag::ext_c11_feature) << Tok.getName();
       isInvalid = DS.SetStorageClassSpecThread(DeclSpec::TSCS__Thread_local,
                                                Loc, PrevSpec, DiagID);
       isStorageClass = true;
@@ -3623,7 +3625,7 @@
     // alignment-specifier
     case tok::kw__Alignas:
       if (!getLangOpts().C11)
-        Diag(Tok, diag::ext_c11_alignment) << Tok.getName();
+        Diag(Tok, diag::ext_c11_feature) << Tok.getName();
       ParseAlignmentSpecifier(DS.getAttributes());
       continue;
 
Index: clang/lib/Parse/ParseExpr.cpp
===================================================================
--- clang/lib/Parse/ParseExpr.cpp
+++ clang/lib/Parse/ParseExpr.cpp
@@ -1191,7 +1191,7 @@
   }
   case tok::kw__Alignof:   // unary-expression: '_Alignof' '(' type-name ')'
     if (!getLangOpts().C11)
-      Diag(Tok, diag::ext_c11_alignment) << Tok.getName();
+      Diag(Tok, diag::ext_c11_feature) << Tok.getName();
     LLVM_FALLTHROUGH;
   case tok::kw_alignof:    // unary-expression: 'alignof' '(' type-id ')'
   case tok::kw___alignof:  // unary-expression: '__alignof' unary-expression
Index: clang/test/PCH/thread-local.cpp
===================================================================
--- clang/test/PCH/thread-local.cpp
+++ clang/test/PCH/thread-local.cpp
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -pedantic-errors -std=c++11 -triple x86_64-linux-gnu -emit-pch %s -o %t
-// RUN: %clang_cc1 -pedantic-errors -std=c++11 -triple x86_64-linux-gnu -include-pch %t -verify %s
+// RUN: %clang_cc1 -pedantic-errors -Wno-c11-extensions -std=c++11 -triple x86_64-linux-gnu -emit-pch %s -o %t
+// RUN: %clang_cc1 -pedantic-errors -Wno-c11-extensions -std=c++11 -triple x86_64-linux-gnu -include-pch %t -verify %s
 // REQUIRES: x86-registered-target
 #ifndef HEADER_INCLUDED
 
Index: clang/test/Sema/thread-specifier.c
===================================================================
--- clang/test/Sema/thread-specifier.c
+++ clang/test/Sema/thread-specifier.c
@@ -1,9 +1,10 @@
 // RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic %s -DGNU
 // RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic -x c++ %s -DGNU -std=c++98
-// RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic %s -DC11 -D__thread=_Thread_local
-// RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic -x c++ %s -DC11 -D__thread=_Thread_local -std=c++98
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic %s -std=c11 -DC11 -D__thread=_Thread_local
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic -x c++ %s -DC11 -D__thread=_Thread_local -std=c++98 -DWARN_ON_THREAD_LOCAL
 // RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic -x c++ %s -DCXX11 -D__thread=thread_local -std=c++11 -Wno-deprecated
-// RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic -x c++ %s -DC11 -D__thread=_Thread_local -std=c++11 -Wno-deprecated
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic -x c++ %s -DC11 -D__thread=_Thread_local -std=c++11 -Wno-deprecated -DWARN_ON_THREAD_LOCAL
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify -pedantic %s -std=c99 -D__thread=_Thread_local -DWARN_ON_THREAD_LOCAL -DC99
 
 #ifdef __cplusplus
 // In C++, we define __private_extern__ to extern.
@@ -30,7 +31,7 @@
 __thread int t6();
 #if defined(GNU)
 // expected-error@-2 {{'__thread' is only allowed on variable declarations}}
-#elif defined(C11)
+#elif defined(C11) || defined(C99)
 // expected-error@-4 {{'_Thread_local' is only allowed on variable declarations}}
 #else
 // expected-error@-6 {{'thread_local' is only allowed on variable declarations}}
@@ -40,7 +41,7 @@
   __thread int t8;
 #if defined(GNU)
   // expected-error@-2 {{'__thread' variables must have global storage}}
-#elif defined(C11)
+#elif defined(C11) || defined(C99)
   // expected-error@-4 {{'_Thread_local' variables must have global storage}}
 #endif
   extern __thread int t9;
@@ -121,3 +122,41 @@
 #endif
 
 __thread int aggregate[10] = {0};
+
+#ifdef WARN_ON_THREAD_LOCAL
+// expected-warning@14 {{_Thread_local is a C11-specific feature}}
+// expected-warning@15 {{_Thread_local is a C11-specific feature}}
+// expected-warning@16 {{_Thread_local is a C11-specific feature}}
+// expected-warning@22 {{_Thread_local is a C11-specific feature}}
+// expected-warning@23 {{_Thread_local is a C11-specific feature}}
+// expected-warning@31 {{_Thread_local is a C11-specific feature}}
+// expected-warning@40 {{_Thread_local is a C11-specific feature}}
+// expected-warning@41 {{_Thread_local is a C11-specific feature}}
+// expected-warning@47 {{_Thread_local is a C11-specific feature}}
+// expected-warning@48 {{_Thread_local is a C11-specific feature}}
+// expected-warning@49 {{_Thread_local is a C11-specific feature}}
+#if __cplusplus < 201103L
+// expected-warning@51 {{_Thread_local is a C11-specific feature}}
+// expected-warning@52 {{_Thread_local is a C11-specific feature}}
+#elif !defined(CXX11)
+// expected-warning@54 {{_Thread_local is a C11-specific feature}}
+// expected-warning@55 {{_Thread_local is a C11-specific feature}}
+#endif
+// expected-warning@57 {{_Thread_local is a C11-specific feature}}
+// expected-warning@58 {{_Thread_local is a C11-specific feature}}
+// expected-warning@61 {{_Thread_local is a C11-specific feature}}
+// expected-warning@62 {{_Thread_local is a C11-specific feature}}
+// expected-warning@65 {{_Thread_local is a C11-specific feature}}
+// expected-warning@75 {{_Thread_local is a C11-specific feature}}
+// expected-warning@88 {{_Thread_local is a C11-specific feature}}
+#ifdef __cplusplus
+// expected-warning@102 {{_Thread_local is a C11-specific feature}}
+// expected-warning@115 {{_Thread_local is a C11-specific feature}}
+#endif
+// expected-warning@124 {{_Thread_local is a C11-specific feature}}
+#endif
+#ifdef CXX11
+// expected-warning@69 {{_Thread_local is a C11-specific feature}}
+// expected-warning@70 {{_Thread_local is a C11-specific feature}}
+#endif
+
Index: clang/test/SemaOpenCLCXX/restricted.cl
===================================================================
--- clang/test/SemaOpenCLCXX/restricted.cl
+++ clang/test/SemaOpenCLCXX/restricted.cl
@@ -31,6 +31,8 @@
 // Test storage class qualifiers.
 __constant _Thread_local int a = 1;
 // expected-error@-1 {{C++ for OpenCL version 1.0 does not support the '_Thread_local' storage class specifier}}
+// expected-warning@-2 {{_Thread_local is a C11-specific feature}}
+
 __constant __thread int b = 2;
 // expected-error@-1 {{C++ for OpenCL version 1.0 does not support the '__thread' storage class specifier}}
 kernel void test_storage_classes() {