Index: lib/Serialization/ModuleManager.cpp
===================================================================
--- lib/Serialization/ModuleManager.cpp
+++ lib/Serialization/ModuleManager.cpp
@@ -161,21 +161,24 @@
   if (std::unique_ptr<llvm::MemoryBuffer> Buffer = lookupBuffer(FileName)) {
     // The buffer was already provided for us.
     NewModule->Buffer = &PCMCache->addBuffer(FileName, std::move(Buffer));
+    // Since the cached buffer is reused, it is safe to close the file
+    // descriptor that was opened while stat()ing the PCM in
+    // lookupModuleFile() above, it won't be needed any longer.
+    Entry->closeFile();
   } else if (llvm::MemoryBuffer *Buffer = PCMCache->lookupBuffer(FileName)) {
     NewModule->Buffer = Buffer;
+    // As above, the file descriptor is no longer needed.
+    Entry->closeFile();
   } else {
     // Open the AST file.
     llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Buf((std::error_code()));
     if (FileName == "-") {
       Buf = llvm::MemoryBuffer::getSTDIN();
     } else {
-      // Leave the FileEntry open so if it gets read again by another
-      // ModuleManager it must be the same underlying file.
-      // FIXME: Because FileManager::getFile() doesn't guarantee that it will
-      // give us an open file, this may not be 100% reliable.
+      // Get a buffer of the file and close the file descriptor when done.
       Buf = FileMgr.getBufferForFile(NewModule->File,
                                      /*IsVolatile=*/false,
-                                     /*ShouldClose=*/false);
+                                     /*ShouldClose=*/true);
     }
 
     if (!Buf) {