Index: lib/Basic/SourceManager.cpp
===================================================================
--- lib/Basic/SourceManager.cpp
+++ lib/Basic/SourceManager.cpp
@@ -125,11 +125,12 @@
   // possible.
   if (!BufferOrError) {
     StringRef FillStr("<<<MISSING SOURCE FILE>>>\n");
-    Buffer.setPointer(MemoryBuffer::getNewUninitMemBuffer(
-                          ContentsEntry->getSize(), "<invalid>").release());
-    char *Ptr = const_cast<char*>(Buffer.getPointer()->getBufferStart());
+    auto BackupBuffer = llvm::WritableMemoryBuffer::getNewUninitMemBuffer(
+        ContentsEntry->getSize(), "<invalid>");
+    char *Ptr = BackupBuffer->getBufferStart();
     for (unsigned i = 0, e = ContentsEntry->getSize(); i != e; ++i)
       Ptr[i] = FillStr[i % FillStr.size()];
+    Buffer.setPointer(BackupBuffer.release());
 
     if (Diag.isDiagnosticInFlight())
       Diag.SetDelayedDiagnostic(diag::err_cannot_open_file,
Index: lib/Lex/Preprocessor.cpp
===================================================================
--- lib/Lex/Preprocessor.cpp
+++ lib/Lex/Preprocessor.cpp
@@ -420,10 +420,9 @@
   CodeCompletionFile = File;
   CodeCompletionOffset = Position - Buffer->getBufferStart();
 
-  std::unique_ptr<MemoryBuffer> NewBuffer =
-      MemoryBuffer::getNewUninitMemBuffer(Buffer->getBufferSize() + 1,
-                                          Buffer->getBufferIdentifier());
-  char *NewBuf = const_cast<char*>(NewBuffer->getBufferStart());
+  auto NewBuffer = llvm::WritableMemoryBuffer::getNewUninitMemBuffer(
+      Buffer->getBufferSize() + 1, Buffer->getBufferIdentifier());
+  char *NewBuf = NewBuffer->getBufferStart();
   char *NewPos = std::copy(Buffer->getBufferStart(), Position, NewBuf);
   *NewPos = '\0';
   std::copy(Position, Buffer->getBufferEnd(), NewPos+1);