Index: llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
===================================================================
--- llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
+++ llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
@@ -38,12 +38,12 @@
 
 static uint32_t calculateDiSymbolStreamSize(uint32_t SymbolByteSize,
                                             uint32_t C13Size) {
-  uint32_t Size = sizeof(uint32_t); // Signature
-  Size += SymbolByteSize;           // Symbol Data
-  Size += 0;                        // TODO: Layout.C11Bytes
-  Size += C13Size;                  // C13 Debug Info Size
-  Size += sizeof(uint32_t);         // GlobalRefs substream size (always 0)
-  Size += 0;                        // GlobalRefs substream bytes
+  uint32_t Size = sizeof(uint32_t);   // Signature
+  Size += alignTo(SymbolByteSize, 4); // Symbol Data
+  Size += 0;                          // TODO: Layout.C11Bytes
+  Size += C13Size;                    // C13 Debug Info Size
+  Size += sizeof(uint32_t);           // GlobalRefs substream size (always 0)
+  Size += 0;                          // GlobalRefs substream bytes
   return Size;
 }
 
@@ -110,7 +110,7 @@
 
   // This value includes both the signature field as well as the record bytes
   // from the symbol stream.
-  Layout.SymBytes = SymbolByteSize + sizeof(uint32_t);
+  Layout.SymBytes = alignTo(SymbolByteSize + sizeof(uint32_t), 4);
 }
 
 Error DbiModuleDescriptorBuilder::finalizeMsfLayout() {
@@ -152,13 +152,17 @@
     BinaryStreamRef RecordsRef(Records);
     if (auto EC = SymbolWriter.writeStreamRef(RecordsRef))
       return EC;
+    if (auto EC = SymbolWriter.padToAlignment(4))
+      return EC;
     // TODO: Write C11 Line data
 
     for (const auto &Builder : C13Builders) {
+      assert(SymbolWriter.getOffset() % 4 == 0);
       assert(Builder && "Empty C13 Fragment Builder!");
       if (auto EC = Builder->commit(SymbolWriter))
         return EC;
     }
+    assert(SymbolWriter.getOffset() % 4 == 0);
 
     // TODO: Figure out what GlobalRefs substream actually is and populate it.
     if (auto EC = SymbolWriter.writeInteger<uint32_t>(0))