Index: clang/include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ clang/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: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -5500,10 +5500,17 @@
   if (VolatileOptionID == options::OPT__SLASH_volatile_ms)
     CmdArgs.push_back("-fms-volatile");
 
- if (Args.hasFlag(options::OPT__SLASH_Zc_dllexportInlines_,
-                  options::OPT__SLASH_Zc_dllexportInlines,
-                  false))
+  if (Args.hasFlag(options::OPT__SLASH_Zc_dllexportInlines_,
+                   options::OPT__SLASH_Zc_dllexportInlines,
+                   false)) {
     CmdArgs.push_back("-fno-dllexport-inlines");
+    if (Args.hasArg(options::OPT__SLASH_fallback)) {
+      const Arg *dllexportInlines =
+        Args.getLastArg(options::OPT__SLASH_Zc_dllexportInlines_);
+      D.Diag(clang::diag::warn_drv_non_fallback_argument_clang_cl)
+        << dllexportInlines->getAsString(Args);
+    }
+  }
 
   Arg *MostGeneralArg = Args.getLastArg(options::OPT__SLASH_vmg);
   Arg *BestCaseArg = Args.getLastArg(options::OPT__SLASH_vmb);
Index: clang/test/Driver/cl-options.c
===================================================================
--- clang/test/Driver/cl-options.c
+++ clang/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"