6 files changed, 34 insertions, 2 deletions
diff --git a/clang/test/Headers/c11.c b/clang/test/Headers/c11.c
index b7b15011f3c..6594823c273 100644
--- a/clang/test/Headers/c11.c
+++ b/clang/test/Headers/c11.c
@@ -1,6 +1,6 @@
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c11 %s
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -fmodules -fmodules-cache-path=%t %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -fmodules -fmodules-cache-path=%t %s -D__STDC_WANT_LIB_EXT1__=1
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -ffreestanding %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -triple i686-pc-win32 -fms-compatibility-version=17.00 %s
 
diff --git a/clang/test/Modules/Inputs/StdDef/include_again.h b/clang/test/Modules/Inputs/StdDef/include_again.h
new file mode 100644
index 00000000000..f29f6366cc6
--- /dev/null
+++ b/clang/test/Modules/Inputs/StdDef/include_again.h
@@ -0,0 +1,2 @@
+#include <stddef.h>
+
diff --git a/clang/test/Modules/Inputs/StdDef/module.map b/clang/test/Modules/Inputs/StdDef/module.map
index 69c69eac35b..5c4e0dae7ba 100644
--- a/clang/test/Modules/Inputs/StdDef/module.map
+++ b/clang/test/Modules/Inputs/StdDef/module.map
@@ -8,4 +8,14 @@ module StdDef {
     header "other.h"
     export *
   }
+
+  module PtrDiffT {
+    header "ptrdiff_t.h"
+    export *
+  }
+
+  module IncludeAgain {
+    header "include_again.h"
+    export *
+  }
 }
diff --git a/clang/test/Modules/Inputs/StdDef/ptrdiff_t.h b/clang/test/Modules/Inputs/StdDef/ptrdiff_t.h
new file mode 100644
index 00000000000..acb0ab81ffc
--- /dev/null
+++ b/clang/test/Modules/Inputs/StdDef/ptrdiff_t.h
@@ -0,0 +1,2 @@
+#define __need_ptrdiff_t
+#include <stddef.h>
diff --git a/clang/test/Modules/stddef.c b/clang/test/Modules/stddef.c
new file mode 100644
index 00000000000..aefc90f9a11
--- /dev/null
+++ b/clang/test/Modules/stddef.c
@@ -0,0 +1,13 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I%S/Inputs/StdDef %s -verify -fno-modules-error-recovery
+
+#include "ptrdiff_t.h"
+
+ptrdiff_t pdt;
+
+size_t st; // expected-error {{must be imported}}
+// expected-note@stddef.h:* {{previous}}
+
+#include "include_again.h"
+
+size_t st2;
diff --git a/clang/test/Modules/system_headers.m b/clang/test/Modules/system_headers.m
index 39b13ca5fc4..8adc7e85769 100644
--- a/clang/test/Modules/system_headers.m
+++ b/clang/test/Modules/system_headers.m
@@ -1,8 +1,13 @@
 // Test that system-headerness works for building modules.
 
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t/cache -isystem %S/Inputs -pedantic -Werror %s -verify
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t/cache -isystem %S/Inputs -pedantic -Werror %s -verify -std=c11
 // expected-no-diagnostics
 
 @import warning;
 int i = bigger_than_int;
+
+#include <stddef.h>
+
+#define __need_size_t
+#include <stddef.h>