Index: include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
===================================================================
--- include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
+++ include/llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h
@@ -44,6 +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;
 
Index: include/llvm/DebugInfo/PDB/Raw/PDBFileBuilder.h
===================================================================
--- include/llvm/DebugInfo/PDB/Raw/PDBFileBuilder.h
+++ include/llvm/DebugInfo/PDB/Raw/PDBFileBuilder.h
@@ -44,6 +44,9 @@
   TpiStreamBuilder &getTpiBuilder();
   TpiStreamBuilder &getIpiBuilder();
 
+  // Add given bytes as a new stream. Returns the stream index.
+  Expected<uint32_t> addStream(ArrayRef<uint8_t> Data);
+
   Expected<std::unique_ptr<PDBFile>>
   build(std::unique_ptr<msf::WritableStream> PdbFileBuffer);
 
@@ -59,6 +62,7 @@
   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
@@ -44,6 +44,10 @@
 
 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() +
Index: lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
===================================================================
--- lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
+++ lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
@@ -66,6 +66,16 @@
   return *Ipi;
 }
 
+Expected<uint32_t> PDBFileBuilder::addStream(ArrayRef<uint8_t> Data) {
+  auto ExpectedIndex = Msf->addStream(Data.size());
+  if (!ExpectedIndex)
+    return ExpectedIndex.takeError();
+  uint32_t Index = std::move(*ExpectedIndex);
+
+  Streams.emplace_back(Data, Index);
+  return *ExpectedIndex;
+}
+
 Expected<msf::MSFLayout> PDBFileBuilder::finalizeMsfLayout() const {
   if (Info) {
     if (auto EC = Info->finalizeMsfLayout())
@@ -189,5 +199,14 @@
       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();
 }