diff --git a/llvm/include/llvm/ProfileData/InstrProf.h b/llvm/include/llvm/ProfileData/InstrProf.h
--- a/llvm/include/llvm/ProfileData/InstrProf.h
+++ b/llvm/include/llvm/ProfileData/InstrProf.h
@@ -1028,6 +1028,16 @@
   uint64_t Unused; // Becomes unused since version 4
   uint64_t HashType;
   uint64_t HashOffset;
+  // New fields should only be added at the end to ensure that the size
+  // computation is correct. The methods below need to be updated to ensure that
+  // the new field is read correctly.
+
+  // Reads a header struct from the buffer.
+  static Expected<Header> readFromBuffer(const unsigned char *Buffer);
+
+  // Returns the size of the header in bytes for all valid fields based on the
+  // version. I.e a older version header will return a smaller size.
+  size_t size() const;
 };
 
 // Profile summary data recorded in the profile data file in indexed
diff --git a/llvm/lib/ProfileData/InstrProf.cpp b/llvm/lib/ProfileData/InstrProf.cpp
--- a/llvm/lib/ProfileData/InstrProf.cpp
+++ b/llvm/lib/ProfileData/InstrProf.cpp
@@ -51,6 +51,7 @@
 #include <memory>
 #include <string>
 #include <system_error>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -1311,4 +1312,59 @@
   }
 }
 
+namespace IndexedInstrProf {
+// A C++14 compatible version of the offsetof macro.
+template <typename T1, typename T2>
+inline size_t constexpr offsetOf(T1 T2::*Member) {
+  constexpr T2 Object{};
+  return size_t(&(Object.*Member)) - size_t(&Object);
+}
+
+static inline uint64_t read(const unsigned char *Buffer, size_t Offset) {
+  return *reinterpret_cast<const uint64_t *>(Buffer + Offset);
+}
+
+Expected<Header> Header::readFromBuffer(const unsigned char *Buffer) {
+  using namespace support;
+  static_assert(std::is_standard_layout<Header>::value,
+                "The header should be standard layout type since we use offset "
+                "of fields to read.");
+  Header H;
+
+  H.Magic = read(Buffer, offsetOf(&Header::Magic));
+  // Check the magic number.
+  uint64_t Magic = endian::byte_swap<uint64_t, little>(H.Magic);
+  if (Magic != IndexedInstrProf::Magic)
+    return make_error<InstrProfError>(instrprof_error::bad_magic);
+
+  // Read the version.
+  H.Version = read(Buffer, offsetOf(&Header::Version));
+  uint64_t FormatVersion = endian::byte_swap<uint64_t, little>(H.Version);
+  if (GET_VERSION(FormatVersion) >
+      IndexedInstrProf::ProfVersion::CurrentVersion)
+    return make_error<InstrProfError>(instrprof_error::unsupported_version);
+
+  switch (GET_VERSION(FormatVersion)) {
+  // When a new field is added in the header add a case statement here to
+  // populate it.
+  default:
+    H.HashType = read(Buffer, offsetOf(&Header::HashType));
+    H.HashOffset = read(Buffer, offsetOf(&Header::HashOffset));
+  }
+
+  return H;
+}
+
+size_t Header::size() const {
+  switch (GET_VERSION(Version)) {
+  // When a new field is added to the header add a case statement here to
+  // compute the size as offset of the new field + size of the new field. This
+  // relies on the field being added to the end of the list.
+  default:
+    return offsetOf(&Header::HashOffset) + sizeof(Header::HashOffset);
+  }
+}
+
+} // namespace IndexedInstrProf
+
 } // end namespace llvm
diff --git a/llvm/lib/ProfileData/InstrProfReader.cpp b/llvm/lib/ProfileData/InstrProfReader.cpp
--- a/llvm/lib/ProfileData/InstrProfReader.cpp
+++ b/llvm/lib/ProfileData/InstrProfReader.cpp
@@ -934,24 +934,17 @@
   if ((const unsigned char *)DataBuffer->getBufferEnd() - Cur < 24)
     return error(instrprof_error::truncated);
 
-  auto *Header = reinterpret_cast<const IndexedInstrProf::Header *>(Cur);
-  Cur += sizeof(IndexedInstrProf::Header);
+  auto HeaderOr = IndexedInstrProf::Header::readFromBuffer(Start);
+  if (!HeaderOr)
+    return HeaderOr.takeError();
 
-  // Check the magic number.
-  uint64_t Magic = endian::byte_swap<uint64_t, little>(Header->Magic);
-  if (Magic != IndexedInstrProf::Magic)
-    return error(instrprof_error::bad_magic);
-
-  // Read the version.
-  uint64_t FormatVersion = endian::byte_swap<uint64_t, little>(Header->Version);
-  if (GET_VERSION(FormatVersion) >
-      IndexedInstrProf::ProfVersion::CurrentVersion)
-    return error(instrprof_error::unsupported_version);
+  const IndexedInstrProf::Header *Header = &HeaderOr.get();
+  Cur += Header->size();
 
-  Cur = readSummary((IndexedInstrProf::ProfVersion)FormatVersion, Cur,
+  Cur = readSummary((IndexedInstrProf::ProfVersion)Header->Version, Cur,
                     /* UseCS */ false);
-  if (FormatVersion & VARIANT_MASK_CSIR_PROF)
-    Cur = readSummary((IndexedInstrProf::ProfVersion)FormatVersion, Cur,
+  if (Header->Version & VARIANT_MASK_CSIR_PROF)
+    Cur = readSummary((IndexedInstrProf::ProfVersion)Header->Version, Cur,
                       /* UseCS */ true);
 
   // Read the hash type and start offset.
@@ -963,9 +956,8 @@
   uint64_t HashOffset = endian::byte_swap<uint64_t, little>(Header->HashOffset);
 
   // The rest of the file is an on disk hash table.
-  auto IndexPtr =
-      std::make_unique<InstrProfReaderIndex<OnDiskHashTableImplV3>>(
-          Start + HashOffset, Cur, Start, HashType, FormatVersion);
+  auto IndexPtr = std::make_unique<InstrProfReaderIndex<OnDiskHashTableImplV3>>(
+      Start + HashOffset, Cur, Start, HashType, Header->Version);
 
   // Load the remapping table now if requested.
   if (RemappingBuffer) {