diff --git a/llvm/include/llvm/Support/raw_ostream.h b/llvm/include/llvm/Support/raw_ostream.h
index f87344e860518..70916d8e4adb0 100644
--- a/llvm/include/llvm/Support/raw_ostream.h
+++ b/llvm/include/llvm/Support/raw_ostream.h
@@ -739,7 +739,7 @@ class LLVM_ABI raw_null_ostream : public raw_pwrite_stream {
   uint64_t current_pos() const override;
 
 public:
-  explicit raw_null_ostream() = default;
+  explicit raw_null_ostream() : raw_pwrite_stream(/*Unbuffered=*/true) {}
   ~raw_null_ostream() override;
 };
 
diff --git a/llvm/unittests/Support/raw_ostream_test.cpp b/llvm/unittests/Support/raw_ostream_test.cpp
index fbeff37d26a35..8f9ed4143a873 100644
--- a/llvm/unittests/Support/raw_ostream_test.cpp
+++ b/llvm/unittests/Support/raw_ostream_test.cpp
@@ -626,6 +626,11 @@ TEST(raw_ostreamTest, writeToDevNull) {
   EXPECT_TRUE(DevNullIsUsed);
 }
 
+TEST(raw_ostreamTest, nullStreamZeroBufferSize) {
+  raw_ostream &NullStream = nulls();
+  EXPECT_EQ(NullStream.GetBufferSize(), 0u);
+}
+
 TEST(raw_ostreamTest, writeToStdOut) {
   outs().flush();
   testing::internal::CaptureStdout();