diff --git a/llvm/include/llvm/BinaryFormat/XCOFF.h b/llvm/include/llvm/BinaryFormat/XCOFF.h
--- a/llvm/include/llvm/BinaryFormat/XCOFF.h
+++ b/llvm/include/llvm/BinaryFormat/XCOFF.h
@@ -26,8 +26,13 @@
 
 constexpr size_t FileNamePadSize = 6;
 constexpr size_t NameSize = 8;
+constexpr size_t FileHeaderSize32 = 20;
+constexpr size_t FileHeaderSize64 = 24;
+constexpr size_t SectionHeaderSize32 = 40;
+constexpr size_t SectionHeaderSize64 = 72;
 constexpr size_t SymbolTableEntrySize = 18;
 constexpr size_t RelocationSerializationSize32 = 10;
+constexpr size_t RelocationSerializationSize64 = 14;
 constexpr uint16_t RelocOverflow = 65535;
 constexpr uint8_t AllocRegNo = 31;
 
@@ -255,29 +260,6 @@
                 ///< large code model TOC-relative relocation.
 };
 
-struct FileHeader32 {
-  uint16_t Magic;
-  uint16_t NumberOfSections;
-  int32_t TimeStamp;
-  uint32_t SymbolTableFileOffset;
-  int32_t NumberOfSymbolTableEntries;
-  uint16_t AuxiliaryHeaderSize;
-  uint16_t Flags;
-};
-
-struct SectionHeader32 {
-  char Name[XCOFF::NameSize];
-  uint32_t PhysicalAddress;
-  uint32_t VirtualAddress;
-  uint32_t Size;
-  uint32_t FileOffsetToData;
-  uint32_t FileOffsetToRelocations;
-  uint32_t FileOffsetToLineNumbers;
-  uint16_t NumberOfRelocations;
-  uint16_t NumberOfLineNumbers;
-  int32_t Flags;
-};
-
 enum CFileStringType : uint8_t {
   XFT_FN = 0,  ///< Specifies the source-file name.
   XFT_CT = 1,  ///< Specifies the compiler time stamp.
diff --git a/llvm/lib/MC/XCOFFObjectWriter.cpp b/llvm/lib/MC/XCOFFObjectWriter.cpp
--- a/llvm/lib/MC/XCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/XCOFFObjectWriter.cpp
@@ -922,8 +922,8 @@
   SymbolTableEntryCount = SymbolTableIndex;
 
   // Calculate the RawPointer value for each section.
-  uint64_t RawPointer = sizeof(XCOFF::FileHeader32) + auxiliaryHeaderSize() +
-                        SectionCount * sizeof(XCOFF::SectionHeader32);
+  uint64_t RawPointer = XCOFF::FileHeaderSize32 + auxiliaryHeaderSize() +
+                        SectionCount * XCOFF::SectionHeaderSize32;
   for (auto *Sec : Sections) {
     if (Sec->Index == Section::UninitializedIndex || Sec->IsVirtual)
       continue;