Index: include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- include/clang/Basic/DiagnosticDriverKinds.td
+++ include/clang/Basic/DiagnosticDriverKinds.td
@@ -161,6 +161,10 @@
   "support for '/Yc' with more than one source file not implemented yet; flag ignored">,
   InGroup<ClangClPch>;
 
+def warn_drv_non_fallback_argument_clang_cl : Warning<
+  "option '%0' is ignored when /fallback happens">,
+  InGroup<OptionIgnored>;
+
 def err_drv_invalid_value : Error<"invalid value '%1' in '%0'">;
 def err_drv_invalid_int_value : Error<"invalid integral value '%1' in '%0'">;
 def err_drv_invalid_remap_file : Error<
Index: lib/Driver/ToolChains/MSVC.cpp
===================================================================
--- lib/Driver/ToolChains/MSVC.cpp
+++ lib/Driver/ToolChains/MSVC.cpp
@@ -669,6 +669,12 @@
   // them too.
   Args.AddAllArgs(CmdArgs, options::OPT_UNKNOWN);
 
+  // Warning for ignored flag.
+  if (const Arg *dllexportInlines =
+      Args.getLastArg(options::OPT__SLASH_Zc_dllexportInlines_))
+    C.getDriver().Diag(clang::diag::warn_drv_non_fallback_argument_clang_cl)
+      << dllexportInlines->getAsString(Args);
+
   // Input filename.
   assert(Inputs.size() == 1);
   const InputInfo &II = Inputs[0];
Index: test/Driver/cl-options.c
===================================================================
--- test/Driver/cl-options.c
+++ test/Driver/cl-options.c
@@ -494,6 +494,8 @@
 // NoDllExportInlines: "-fno-dllexport-inlines"
 // RUN: %clang_cl /Zc:dllexportInlines /c -### -- %s 2>&1 | FileCheck -check-prefix=DllExportInlines %s
 // DllExportInlines-NOT: "-fno-dllexport-inlines"
+// RUN: %clang_cl /fallback /Zc:dllexportInlines- /c -### -- %s 2>&1 | FileCheck -check-prefix=DllExportInlinesFallback %s
+// DllExportInlinesFallback: warning: option '/Zc:dllexportInlines-' is ignored when /fallback happens [-Woption-ignored]
 
 // RUN: %clang_cl /Zi /c -### -- %s 2>&1 | FileCheck -check-prefix=Zi %s
 // Zi: "-gcodeview"