diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index 529c971..018a0b8 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -89,7 +89,9 @@
                      HeaderSearch &HeaderInfo)
     : SourceMgr(SourceMgr), Diags(Diags), LangOpts(LangOpts), Target(Target),
       HeaderInfo(HeaderInfo), BuiltinIncludeDir(nullptr),
-      CompilingModule(nullptr), SourceModule(nullptr) {}
+      CompilingModule(nullptr), SourceModule(nullptr) {
+  MMapLangOpts.LineComment = true;
+}
 
 ModuleMap::~ModuleMap() {
   for (llvm::StringMap<Module *>::iterator I = Modules.begin(),