Index: clang/lib/Lex/ModuleMap.cpp
===================================================================
--- clang/lib/Lex/ModuleMap.cpp
+++ clang/lib/Lex/ModuleMap.cpp
@@ -379,6 +379,7 @@
 bool ModuleMap::isBuiltinHeader(StringRef FileName) {
   return llvm::StringSwitch<bool>(FileName)
            .Case("float.h", true)
+           .Case("inttypes.h", true)
            .Case("iso646.h", true)
            .Case("limits.h", true)
            .Case("stdalign.h", true)
Index: clang/test/Modules/Inputs/System/usr/include/module.map
===================================================================
--- clang/test/Modules/Inputs/System/usr/include/module.map
+++ clang/test/Modules/Inputs/System/usr/include/module.map
@@ -4,6 +4,11 @@
     header "float.h"
   }
 
+  // In both directories (compiler support version wins, forwards)
+  module inttypes {
+    header "inttypes.h"
+  }
+
   // Only in system headers directory
   module stdio {
     header "stdio.h"
Index: clang/test/Modules/Werror-Wsystem-headers.m
===================================================================
--- clang/test/Modules/Werror-Wsystem-headers.m
+++ clang/test/Modules/Werror-Wsystem-headers.m
@@ -4,17 +4,17 @@
 
 // Initial module build
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -fdisable-module-hash \
-// RUN:     -isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify
+// RUN:     -internal-isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify
 // RUN: cp %t/cstd.pcm %t-saved/cstd.pcm
 
 // Even with -Werror don't rebuild a system module
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -fdisable-module-hash \
-// RUN:     -isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify -Werror
+// RUN:     -internal-isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify -Werror
 // RUN: diff %t/cstd.pcm %t-saved/cstd.pcm
 
 // Unless -Wsystem-headers is on
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -fdisable-module-hash \
-// RUN:     -isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify \
+// RUN:     -internal-isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify \
 // RUN:     -Werror=unused -Wsystem-headers
 // RUN: not diff %t/cstd.pcm %t-saved/cstd.pcm
 
Index: clang/test/Modules/crash-vfs-include-pch.m
===================================================================
--- clang/test/Modules/crash-vfs-include-pch.m
+++ clang/test/Modules/crash-vfs-include-pch.m
@@ -6,12 +6,12 @@
 // RUN: %clang_cc1 -x objective-c-header -emit-pch %S/Inputs/pch-used.h \
 // RUN:     -o %t/out/pch-used.h.pch -fmodules -fimplicit-module-maps \
 // RUN:     -fmodules-cache-path=%t/cache -O0 \
-// RUN:     -isystem %S/Inputs/System/usr/include
+// RUN:     -internal-isystem %S/Inputs/System/usr/include
 
 // RUN: env FORCE_CLANG_DIAGNOSTICS_CRASH= TMPDIR=%t TEMP=%t TMP=%t \
 // RUN: not %clang %s -E -include-pch %t/out/pch-used.h.pch -fmodules -nostdlibinc \
 // RUN:     -fimplicit-module-maps -fmodules-cache-path=%t/cache -O0 \
-// RUN:     -Xclang -fno-validate-pch -isystem %S/Inputs/System/usr/include \
+// RUN:     -Xclang -fno-validate-pch -Xclang -internal-isystem -Xclang %S/Inputs/System/usr/include \
 // RUN:     -o %t/output.E 2>&1 | FileCheck %s
 
 // RUN: FileCheck --check-prefix=CHECKSH %s -input-file %t/crash-vfs-*.sh
Index: clang/test/Modules/cstd.m
===================================================================
--- clang/test/Modules/cstd.m
+++ clang/test/Modules/cstd.m
@@ -28,3 +28,11 @@
 #  error "bool was not defined!"
 #endif
 
+// Supplied by compiler, which forwards to the "/usr/include" version.
+@import cstd.inttypes;
+#ifndef __CLANG_INTTYPES_H
+#error "__CLANG_INTTYPES_H was not defined!"
+#endif
+#ifndef MY_PRIi32
+#error "MY_PRIi32 was not defined!"
+#endif
Index: clang/test/Modules/pch-used.m
===================================================================
--- clang/test/Modules/pch-used.m
+++ clang/test/Modules/pch-used.m
@@ -1,8 +1,8 @@
 // UNSUPPORTED: target={{.*}}-zos{{.*}}, target={{.*}}-aix{{.*}}
 // RUN: rm -rf %t
 // RUN: mkdir %t
-// RUN: %clang_cc1 -x objective-c-header -emit-pch %S/Inputs/pch-used.h -o %t/pch-used.h.pch -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -O0 -isystem %S/Inputs/System/usr/include
-// RUN: %clang_cc1 %s -include-pch %t/pch-used.h.pch -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -O0 -isystem %S/Inputs/System/usr/include -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -x objective-c-header -emit-pch %S/Inputs/pch-used.h -o %t/pch-used.h.pch -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -O0 -internal-isystem %S/Inputs/System/usr/include
+// RUN: %clang_cc1 %s -include-pch %t/pch-used.h.pch -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -O0 -internal-isystem %S/Inputs/System/usr/include -emit-llvm -o - | FileCheck %s
 
 void f(void) { SPXTrace(); }
 void g(void) { double x = DBL_MAX; }