Index: include/llvm/DebugInfo/PDB/Native/DbiStreamBuilder.h
===================================================================
--- include/llvm/DebugInfo/PDB/Native/DbiStreamBuilder.h
+++ include/llvm/DebugInfo/PDB/Native/DbiStreamBuilder.h
@@ -82,6 +82,7 @@
 
   Error finalize();
   uint32_t calculateModiSubstreamSize() const;
+  uint32_t calculateNamesOffset() const;
   uint32_t calculateSectionContribsStreamSize() const;
   uint32_t calculateSectionMapStreamSize() const;
   uint32_t calculateFileInfoSubstreamSize() const;
Index: lib/DebugInfo/PDB/Native/DbiStreamBuilder.cpp
===================================================================
--- lib/DebugInfo/PDB/Native/DbiStreamBuilder.cpp
+++ lib/DebugInfo/PDB/Native/DbiStreamBuilder.cpp
@@ -129,7 +129,7 @@
   return sizeof(SecMapHeader) + sizeof(SecMapEntry) * SectionMap.size();
 }
 
-uint32_t DbiStreamBuilder::calculateFileInfoSubstreamSize() const {
+uint32_t DbiStreamBuilder::calculateNamesOffset() const {
   uint32_t Size = 0;
   Size += sizeof(ulittle16_t);                         // NumModules
   Size += sizeof(ulittle16_t);                         // NumSourceFiles
@@ -139,6 +139,11 @@
   for (const auto &M : ModiList)
     NumFileInfos += M->source_files().size();
   Size += NumFileInfos * sizeof(ulittle32_t); // FileNameOffsets
+  return Size;
+}
+
+uint32_t DbiStreamBuilder::calculateFileInfoSubstreamSize() const {
+  uint32_t Size = calculateNamesOffset();
   Size += calculateNamesBufferSize();
   return alignTo(Size, sizeof(uint32_t));
 }
@@ -157,9 +162,8 @@
 
 Error DbiStreamBuilder::generateFileInfoSubstream() {
   uint32_t Size = calculateFileInfoSubstreamSize();
-  uint32_t NameSize = calculateNamesBufferSize();
   auto Data = Allocator.Allocate<uint8_t>(Size);
-  uint32_t NamesOffset = Size - NameSize;
+  uint32_t NamesOffset = calculateNamesOffset();
 
   FileInfoBuffer = MutableBinaryByteStream(MutableArrayRef<uint8_t>(Data, Size),
                                            llvm::support::little);
@@ -207,6 +211,9 @@
     }
   }
 
+  if (auto EC = NameBufferWriter.padToAlignment(sizeof(uint32_t)))
+    return EC;
+
   if (NameBufferWriter.bytesRemaining() > 0)
     return make_error<RawError>(raw_error_code::invalid_format,
                                 "The names buffer contained unexpected data.");
Index: test/DebugInfo/PDB/Inputs/source-names-1.yaml
===================================================================
--- /dev/null
+++ test/DebugInfo/PDB/Inputs/source-names-1.yaml
@@ -0,0 +1,27 @@
+---
+MSF:             
+  SuperBlock:      
+    BlockSize:       4096
+    FreeBlockMap:    1
+    NumBlocks:       11
+    NumDirectoryBytes: 64
+    Unknown1:        0
+    BlockMapAddr:    3
+  NumDirectoryBlocks: 1
+  DirectoryBlocks: [ 10 ]
+  NumStreams:      0
+  FileSize:        45056
+DbiStream:       
+  VerHeader:       V70
+  Age:             1
+  BuildNumber:     36352
+  PdbDllVersion:   24210
+  PdbDllRbld:      0
+  Flags:           1
+  MachineType:     Amd64
+  Modules:         
+    - Module:          'C:\src\test.obj'
+      ObjFile:         'C:\src\test.obj'
+      SourceFiles:     
+        - 'C:\src\test.c'
+...
Index: test/DebugInfo/PDB/Inputs/source-names-2.yaml
===================================================================
--- /dev/null
+++ test/DebugInfo/PDB/Inputs/source-names-2.yaml
@@ -0,0 +1,27 @@
+---
+MSF:             
+  SuperBlock:      
+    BlockSize:       4096
+    FreeBlockMap:    1
+    NumBlocks:       11
+    NumDirectoryBytes: 64
+    Unknown1:        0
+    BlockMapAddr:    3
+  NumDirectoryBlocks: 1
+  DirectoryBlocks: [ 10 ]
+  NumStreams:      0
+  FileSize:        45056
+DbiStream:       
+  VerHeader:       V70
+  Age:             1
+  BuildNumber:     36352
+  PdbDllVersion:   24210
+  PdbDllRbld:      0
+  Flags:           1
+  MachineType:     Amd64
+  Modules:         
+    - Module:          'C:\src\test.obj'
+      ObjFile:         'C:\src\test.obj'
+      SourceFiles:     
+        - 'C:\src\test.cc'
+...
Index: test/DebugInfo/PDB/pdbdump-align-source-names.test
===================================================================
--- /dev/null
+++ test/DebugInfo/PDB/pdbdump-align-source-names.test
@@ -0,0 +1,20 @@
+# Module source file names are contained in the file info substream. The
+# substream is padded to a multiple of 4 bytes, and this padding must come
+# after the file names. Putting it before the file names results in the
+# possibility of source file names being read as empty or truncated. This test
+# uses file names of two different lengths to make sure at least one hits the
+# case where padding is needed and verifies that file names are correct in
+# both cases.
+
+RUN: llvm-pdbdump yaml2pdb -pdb=%T/source-names-1.pdb %p/Inputs/source-names-1.yaml
+RUN: llvm-pdbdump pdb2yaml -dbi-module-source-info %T/source-names-1.pdb \
+RUN:     | FileCheck -check-prefix=CHECK1 %s
+RUN: llvm-pdbdump yaml2pdb -pdb=%T/source-names-2.pdb %p/Inputs/source-names-2.yaml
+RUN: llvm-pdbdump pdb2yaml -dbi-module-source-info %T/source-names-2.pdb \
+RUN:     | FileCheck -check-prefix=CHECK2 %s
+
+CHECK1: SourceFiles:
+CHECK1: 'C:\src\test.c'
+
+CHECK2: SourceFiles:
+CHECK2: 'C:\src\test.cc'