diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 02a5088..05b3377 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1048,6 +1048,7 @@
   Opts.UsePhonyTargets = Args.hasArg(OPT_MP);
   Opts.ShowHeaderIncludes = Args.hasArg(OPT_H);
   Opts.HeaderIncludeOutputFile = Args.getLastArgValue(OPT_header_include_file);
+  Opts.AddMissingHeaderDeps = Args.hasArg(OPT_MG);
 }
 
 static void ParseDiagnosticArgs(DiagnosticOptions &Opts, ArgList &Args,