diff --git a/llvm/tools/llvm-ml/Opts.td b/llvm/tools/llvm-ml/Opts.td
--- a/llvm/tools/llvm-ml/Opts.td
+++ b/llvm/tools/llvm-ml/Opts.td
@@ -45,6 +45,8 @@
 def assembly_file : MLJoinedOrSeparate<"Ta">,
                     HelpText<"Assemble source file with name not ending with "
                              "the .asm extension">;
+def parse_only : MLFlag<"Zs">, HelpText<"Run a syntax-check only">,
+                 Alias<filetype>, AliasArgs<"none">;
 
 def bitness : LLVMJoined<"m">, Values<"32,64">,
               HelpText<"Target platform (x86 or x86-64)">;
@@ -107,4 +109,3 @@
 def codeview_info : UnsupportedFlag<"Zi">, HelpText<"">;
 def enable_m510_option : UnsupportedFlag<"Zm">, HelpText<"">;
 def structure_packing : UnsupportedJoined<"Zp">, HelpText<"">;
-def parse_only : UnsupportedFlag<"Zs">, HelpText<"">;