Index: clang/include/clang/Frontend/CompilerInstance.h
===================================================================
--- clang/include/clang/Frontend/CompilerInstance.h
+++ clang/include/clang/Frontend/CompilerInstance.h
@@ -171,11 +171,6 @@
     }
   };
 
-  /// If the output doesn't support seeking (terminal, pipe). we switch
-  /// the stream to a buffer_ostream. These are the buffer and the original
-  /// stream.
-  std::unique_ptr<llvm::raw_fd_ostream> NonSeekStream;
-
   /// The list of active output files.
   std::list<OutputFile> OutputFiles;
 
Index: clang/lib/Frontend/CompilerInstance.cpp
===================================================================
--- clang/lib/Frontend/CompilerInstance.cpp
+++ clang/lib/Frontend/CompilerInstance.cpp
@@ -672,7 +672,6 @@
       llvm::sys::fs::remove(Module.second);
     BuiltModules.clear();
   }
-  NonSeekStream.reset();
 }
 
 std::unique_ptr<raw_pwrite_stream>
@@ -803,10 +802,7 @@
   if (!Binary || OS->supportsSeeking())
     return std::move(OS);
 
-  auto B = std::make_unique<llvm::buffer_ostream>(*OS);
-  assert(!NonSeekStream);
-  NonSeekStream = std::move(OS);
-  return std::move(B);
+  return std::make_unique<llvm::buffer_unique_ostream>(std::move(OS));
 }
 
 // Initialization Utilities
Index: llvm/include/llvm/Support/raw_ostream.h
===================================================================
--- llvm/include/llvm/Support/raw_ostream.h
+++ llvm/include/llvm/Support/raw_ostream.h
@@ -687,6 +687,18 @@
   ~buffer_ostream() override { OS << str(); }
 };
 
+class buffer_unique_ostream : public raw_svector_ostream {
+  std::unique_ptr<raw_ostream> OS;
+  SmallVector<char, 0> Buffer;
+
+  virtual void anchor() override;
+
+public:
+  buffer_unique_ostream(std::unique_ptr<raw_ostream> OS)
+      : raw_svector_ostream(Buffer), OS(std::move(OS)) {}
+  ~buffer_unique_ostream() override { *OS << str(); }
+};
+
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_RAW_OSTREAM_H
Index: llvm/lib/Support/raw_ostream.cpp
===================================================================
--- llvm/lib/Support/raw_ostream.cpp
+++ llvm/lib/Support/raw_ostream.cpp
@@ -987,3 +987,5 @@
 void raw_pwrite_stream::anchor() {}
 
 void buffer_ostream::anchor() {}
+
+void buffer_unique_ostream::anchor() {}