Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -543,6 +543,8 @@
   has been deprecated. The flag will be removed in Clang 18.
   ``-ftrivial-auto-var-init=zero`` is now available unconditionally, to be
   compatible with GCC.
+- ``-fmodules-ts`` has been deprecated. The flag will be removed in Clang 17.
+  Please use ``-std=c++20`` or higher to use standard C++ modules instead.
 
 Modified Compiler Flags
 -----------------------
Index: clang/include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -630,6 +630,11 @@
   "command line to use the libc++ standard library instead">,
   InGroup<DiagGroup<"stdlibcxx-not-found">>;
 
+def warn_deprecated_fmodules_ts_flag : Warning<
+  "the '-fmodules-ts' flag is deprecated and it will be removed in Clang 17; "
+  "use '-std=c++20' or higher to use standard C++ modules instead">,
+  InGroup<DiagGroup<"deprecated-module-ts">>;
+
 def err_drv_cannot_mix_options : Error<"cannot specify '%1' along with '%0'">;
 
 def err_drv_invalid_object_mode : Error<
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3634,6 +3634,7 @@
 
   HaveModules |= HaveClangModules;
   if (Args.hasArg(options::OPT_fmodules_ts)) {
+    D.Diag(diag::warn_deprecated_fmodules_ts_flag);
     CmdArgs.push_back("-fmodules-ts");
     HaveModules = true;
   }
Index: clang/test/Driver/modules-ts.cpp
===================================================================
--- clang/test/Driver/modules-ts.cpp
+++ clang/test/Driver/modules-ts.cpp
@@ -2,6 +2,7 @@
 //
 // RUN: %clang -fmodules-ts -x c++-module --precompile %s -o %t.pcm -v 2>&1 | FileCheck %s --check-prefix=CHECK-PRECOMPILE
 //
+// CHECK-PRECOMPILE:  warning: the '-fmodules-ts' flag is deprecated and it will be removed in Clang 17; use '-std=c++20' or higher to use standard C++ modules instead [-Wdeprecated-module-ts]
 // CHECK-PRECOMPILE: -cc1 {{.*}} -emit-module-interface
 // CHECK-PRECOMPILE-SAME: -o {{.*}}.pcm
 // CHECK-PRECOMPILE-SAME: -x c++
@@ -9,8 +10,9 @@
 
 // Check compiling a .pcm file to a .o file.
 //
-// RUN: %clang -fmodules-ts -fintegrated-as %t.pcm -c -o %t.pcm.o -v 2>&1 | FileCheck %s --check-prefix=CHECK-COMPILE
+// RUN: %clang -fmodules-ts -fintegrated-as %t.pcm -c -o %t.pcm.o -v 2>&1 | FileCheck %s --check-prefix=CHECK-COMPILE --check-prefix=CHECK-WARN
 //
+// CHECK-WARN:  warning: the '-fmodules-ts' flag is deprecated and it will be removed in Clang 17; use '-std=c++20' or higher to use standard C++ modules instead [-Wdeprecated-module-ts]
 // CHECK-COMPILE: -cc1 {{.*}} -emit-obj
 // CHECK-COMPILE-SAME: -o {{.*}}.pcm.o
 // CHECK-COMPILE-SAME: -x pcm
@@ -20,6 +22,7 @@
 //
 // RUN: %clang -fmodules-ts -fmodule-file=%t.pcm -fintegrated-as -Dexport= %s -c -o %t.o -v 2>&1 | FileCheck %s --check-prefix=CHECK-USE
 //
+// CHECK-USE:  warning: the '-fmodules-ts' flag is deprecated and it will be removed in Clang 17; use '-std=c++20' or higher to use standard C++ modules instead [-Wdeprecated-module-ts]
 // CHECK-USE: -cc1
 // CHECK-USE-SAME: -emit-obj
 // CHECK-USE-SAME: -fmodule-file={{.*}}.pcm