Index: llvm/include/llvm/DebugInfo/CodeView/GlobalTypeTableBuilder.h
===================================================================
--- llvm/include/llvm/DebugInfo/CodeView/GlobalTypeTableBuilder.h
+++ llvm/include/llvm/DebugInfo/CodeView/GlobalTypeTableBuilder.h
@@ -71,6 +71,9 @@
   template <typename CreateFunc>
   TypeIndex insertRecordAs(GloballyHashedType Hash, size_t RecordSize,
                            CreateFunc Create) {
+    assert(RecordSize < UINT32_MAX && "Record too big");
+    assert(RecordSize % 4 == 0 && "Record is not aligned to 4 bytes!");
+
     auto Result = HashedRecords.try_emplace(Hash, nextTypeIndex());
 
     if (LLVM_UNLIKELY(Result.second /*inserted*/ ||
Index: llvm/lib/DebugInfo/CodeView/TypeStreamMerger.cpp
===================================================================
--- llvm/lib/DebugInfo/CodeView/TypeStreamMerger.cpp
+++ llvm/lib/DebugInfo/CodeView/TypeStreamMerger.cpp
@@ -360,16 +360,18 @@
         [this, Type](MutableArrayRef<uint8_t> Storage) -> ArrayRef<uint8_t> {
       return remapIndices(Type, Storage);
     };
+    unsigned AlignedSize = alignTo(Type.RecordData.size(), 4);
+
     if (LLVM_LIKELY(UseGlobalHashes)) {
       GlobalTypeTableBuilder &Dest =
           isIdRecord(Type.kind()) ? *DestGlobalIdStream : *DestGlobalTypeStream;
       GloballyHashedType H = GlobalHashes[CurIndex.toArrayIndex()];
-      DestIdx = Dest.insertRecordAs(H, Type.RecordData.size(), DoSerialize);
+      DestIdx = Dest.insertRecordAs(H, AlignedSize, DoSerialize);
     } else {
       MergingTypeTableBuilder &Dest =
           isIdRecord(Type.kind()) ? *DestIdStream : *DestTypeStream;
 
-      RemapStorage.resize(Type.RecordData.size());
+      RemapStorage.resize(AlignedSize);
       ArrayRef<uint8_t> Result = DoSerialize(RemapStorage);
       if (!Result.empty())
         DestIdx = Dest.insertRecordBytes(Result);
@@ -386,9 +388,14 @@
 ArrayRef<uint8_t>
 TypeStreamMerger::remapIndices(const CVType &OriginalType,
                                MutableArrayRef<uint8_t> Storage) {
+  unsigned Align = OriginalType.RecordData.size() & 3;
+  unsigned AlignedSize = alignTo(OriginalType.RecordData.size(), 4);
+  assert(Storage.size() == AlignedSize &&
+         "The target buffer size must be aligned on a 4-byte boundary!");
+
   SmallVector<TiReference, 4> Refs;
   discoverTypeIndices(OriginalType.RecordData, Refs);
-  if (Refs.empty())
+  if (Refs.empty() && Align == 0)
     return OriginalType.RecordData;
 
   ::memcpy(Storage.data(), OriginalType.RecordData.data(),
@@ -408,6 +415,13 @@
         return {};
     }
   }
+
+  if (Align > 0) {
+    DestContent = Storage.data() + OriginalType.RecordData.size();
+    for (; Align < 4; ++Align) {
+      DestContent[Align] = LF_PAD0 + Align;
+    }
+  }
   return Storage;
 }
 
Index: llvm/test/tools/llvm-readobj/COFF/codeview-merging-alignement.yaml
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-readobj/COFF/codeview-merging-alignement.yaml
@@ -0,0 +1,56 @@
+# RUN: yaml2obj %s -o=%t.obj
+# RUN: llvm-readobj --codeview-merged-types %t.obj | FileCheck %s
+# RUN: llvm-readobj --codeview-merged-types %t.obj --codeview-ghash | FileCheck %s
+# CHECK: MergedTypeStream [
+# CHECK:   Procedure (0x1000) {
+# CHECK:     TypeLeafKind: LF_PROCEDURE (0x1008)
+# CHECK:     ReturnType: void (0x3)
+# CHECK:     CallingConvention: NearC (0x0)
+# CHECK:     FunctionOptions [ (0x0)
+# CHECK:     ]
+# CHECK:     NumParameters: 0
+# CHECK:     ArgListType: 0x0
+# CHECK:   }
+# CHECK:   ArgList (0x1001) {
+# CHECK:     TypeLeafKind: LF_ARGLIST (0x1201)
+# CHECK:     NumArgs: 0
+# CHECK:     Arguments [
+# CHECK:     ]
+# CHECK:   }
+
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:
+  - Name:            '.debug$T'
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
+    Alignment:       1
+    # It is important to keep the 'SectionData' since the .OBJ is reconstructed from it,
+    # and that triggers an alignement bug in the output .PDB.
+    SectionData:     '040000001000081003000000000000000000000000000600011200000000'
+    Types:
+      - Kind:            LF_PROCEDURE
+        Procedure:
+          ReturnType:      3
+          CallConv:        NearC
+          Options:         [ None ]
+          ParameterCount:  0
+          ArgumentList:    0
+      - Kind:            LF_ARGLIST
+        ArgList:
+          ArgIndices:      [  ]
+symbols:
+  - Name:            '.debug$T'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          30
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+...