Index: include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
===================================================================
--- include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
+++ include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
@@ -19,6 +19,7 @@
 #include "llvm/DebugInfo/PDB/PDBTypes.h"
 #include "llvm/DebugInfo/PDB/Raw/PDBFile.h"
 #include "llvm/DebugInfo/PDB/Raw/RawConstants.h"
+#include "llvm/Support/Endian.h"
 
 namespace llvm {
 namespace msf {
@@ -43,6 +44,7 @@
   void setPdbDllRbld(uint16_t R);
   void setFlags(uint16_t F);
   void setMachineType(PDB_Machine M);
+  void setDebugStreamIndex(DbgHeaderType Type, uint32_t Index);
 
   uint32_t calculateSerializedLength() const;
 
@@ -92,6 +94,8 @@
   msf::WritableStreamRef NamesBuffer;
   msf::MutableByteStream ModInfoBuffer;
   msf::MutableByteStream FileInfoBuffer;
+  std::vector<support::ulittle16_t> DbgStreams = {
+      (size_t)DbgHeaderType::Max, (support::ulittle16_t)0};
 };
 }
 }
Index: include/llvm/DebugInfo/PDB/Raw/PDBFileBuilder.h
===================================================================
--- include/llvm/DebugInfo/PDB/Raw/PDBFileBuilder.h
+++ include/llvm/DebugInfo/PDB/Raw/PDBFileBuilder.h
@@ -14,6 +14,7 @@
 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/DebugInfo/PDB/Raw/PDBFile.h"
+#include "llvm/DebugInfo/PDB/Raw/RawConstants.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/Error.h"
@@ -44,6 +45,9 @@
   TpiStreamBuilder &getTpiBuilder();
   TpiStreamBuilder &getIpiBuilder();
 
+  // Add given bytes as a new stream. Returns the stream index.
+  Error addDbgStream(pdb::DbgHeaderType Type, ArrayRef<uint8_t> Data);
+
   Expected<std::unique_ptr<PDBFile>>
   build(std::unique_ptr<msf::WritableStream> PdbFileBuffer);
 
@@ -59,6 +63,7 @@
   std::unique_ptr<DbiStreamBuilder> Dbi;
   std::unique_ptr<TpiStreamBuilder> Tpi;
   std::unique_ptr<TpiStreamBuilder> Ipi;
+  std::vector<std::pair<ArrayRef<uint8_t>, uint32_t>> Streams;
 };
 }
 }
Index: lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
===================================================================
--- lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
+++ lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
@@ -9,6 +9,7 @@
 
 #include "llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h"
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/DebugInfo/MSF/MSFBuilder.h"
 #include "llvm/DebugInfo/MSF/MappedBlockStream.h"
 #include "llvm/DebugInfo/MSF/StreamWriter.h"
@@ -43,10 +44,15 @@
 
 void DbiStreamBuilder::setMachineType(PDB_Machine M) { MachineType = M; }
 
+void DbiStreamBuilder::setDebugStreamIndex(DbgHeaderType Type, uint32_t Index) {
+  DbgStreams[(int)Type] = Index;
+}
+
 uint32_t DbiStreamBuilder::calculateSerializedLength() const {
   // For now we only support serializing the header.
   return sizeof(DbiStreamHeader) + calculateFileInfoSubstreamSize() +
-         calculateModiSubstreamSize();
+         calculateModiSubstreamSize() +
+         DbgStreams.size() * sizeof(DbgStreams[0]);
 }
 
 Error DbiStreamBuilder::addModuleInfo(StringRef ObjFile, StringRef Module) {
@@ -216,7 +222,7 @@
   H->ECSubstreamSize = 0;
   H->FileInfoSize = FileInfoBuffer.getLength();
   H->ModiSubstreamSize = ModInfoBuffer.getLength();
-  H->OptionalDbgHdrSize = 0;
+  H->OptionalDbgHdrSize = DbgStreams.size() * sizeof(DbgStreams[0]);
   H->SecContrSubstreamSize = 0;
   H->SectionMapSize = 0;
   H->TypeServerSize = 0;
@@ -273,6 +279,8 @@
     return EC;
   if (auto EC = Writer.writeStreamRef(FileInfoBuffer))
     return EC;
+  if (auto EC = Writer.writeArray(ArrayRef<support::ulittle16_t>(DbgStreams)))
+    return EC;
 
   if (Writer.bytesRemaining() > 0)
     return make_error<RawError>(raw_error_code::invalid_format,
Index: lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
===================================================================
--- lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
+++ lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
@@ -66,6 +66,18 @@
   return *Ipi;
 }
 
+Error PDBFileBuilder::addDbgStream(pdb::DbgHeaderType Type,
+                                   ArrayRef<uint8_t> Data) {
+  auto ExpectedIndex = Msf->addStream(Data.size());
+  if (!ExpectedIndex)
+    return ExpectedIndex.takeError();
+  uint32_t Index = std::move(*ExpectedIndex);
+  getDbiBuilder().setDebugStreamIndex(Type, Index);
+
+  Streams.emplace_back(Data, Index);
+  return Error::success();
+}
+
 Expected<msf::MSFLayout> PDBFileBuilder::finalizeMsfLayout() const {
   if (Info) {
     if (auto EC = Info->finalizeMsfLayout())
@@ -189,5 +201,14 @@
       return EC;
   }
 
+  for (auto &Pair : Streams) {
+    ArrayRef<uint8_t> Data = Pair.first;
+    uint32_t Idx = Pair.second;
+    auto Stream = WritableMappedBlockStream::createIndexedStream(Layout, Buffer, Idx);
+    StreamWriter Writer(*Stream);
+    if (auto EC = Writer.writeArray(Data))
+      return EC;
+  }
+
   return Buffer.commit();
 }