diff --git a/clang/lib/Serialization/ModuleManager.cpp b/clang/lib/Serialization/ModuleManager.cpp
index ac98ca0..b073984 100644
--- a/clang/lib/Serialization/ModuleManager.cpp
+++ b/clang/lib/Serialization/ModuleManager.cpp
@@ -227,6 +227,15 @@
   InMemoryBuffers[Entry] = std::move(Buffer);
 }
 
+bool ModuleManager::addKnownModuleFile(StringRef FileName) {
+  const FileEntry *File;
+  if (lookupModuleFile(FileName, 0, 0, File))
+    return true;
+  if (!Modules.count(File))
+    AdditionalKnownModuleFiles.insert(File);
+  return false;
+}
+
 ModuleManager::VisitState *ModuleManager::allocateVisitState() {
   // Fast path: if we have a cached state, use it.
   if (FirstVisitState) {
@@ -263,6 +272,8 @@
 }
 
 void ModuleManager::moduleFileAccepted(ModuleFile *MF) {
+  AdditionalKnownModuleFiles.remove(MF->File);
+
   if (!GlobalIndex || GlobalIndex->loadedModuleFile(MF))
     return;