diff --git a/include/llvm/Bitcode/LLVMBitCodes.h b/include/llvm/Bitcode/LLVMBitCodes.h
index 71f3cc80dd7..1b25ff3768c 100644
--- a/include/llvm/Bitcode/LLVMBitCodes.h
+++ b/include/llvm/Bitcode/LLVMBitCodes.h
@@ -219,6 +219,8 @@ enum GlobalValueSummarySymtabCodes {
   FS_COMBINED_ALIAS = 8,
   // COMBINED_ORIGINAL_NAME: [original_name_hash]
   FS_COMBINED_ORIGINAL_NAME = 9,
+  // VERSION of the summary, bumped when adding flags for instance.
+  FS_VERSION = 10,
 };
 
 enum MetadataCodes {
diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index cbacf8127d4..8b583fe4995 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -5995,8 +5995,21 @@ std::error_code ModuleSummaryIndexBitcodeReader::parseModule() {
 std::error_code ModuleSummaryIndexBitcodeReader::parseEntireSummary() {
   if (Stream.EnterSubBlock(bitc::GLOBALVAL_SUMMARY_BLOCK_ID))
     return error("Invalid record");
-
   SmallVector<uint64_t, 64> Record;
+
+  // Parse version
+  {
+    BitstreamEntry Entry = Stream.advanceSkippingSubblocks();
+    if (Entry.Kind != BitstreamEntry::Record)
+      return error("Invalid Summary Block: record for version expected");
+    if (Stream.readRecord(Entry.ID, Record) != bitc::FS_VERSION)
+      return error("Invalid Summary Block: version expected");
+  }
+  const uint64_t Version = Record[0];
+  if (Version != 1)
+    return error("Invalid summary version " + Twine(Version) + ", 1 expected");
+  Record.clear();
+
   // Keep around the last seen summary to be used when we see an optional
   // "OriginalName" attachement.
   GlobalValueSummary *LastSeenSummary = nullptr;
diff --git a/lib/Bitcode/Writer/BitcodeWriter.cpp b/lib/Bitcode/Writer/BitcodeWriter.cpp
index 302629b9176..d0f87e7d9d0 100644
--- a/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -3067,6 +3067,11 @@ void ModuleBitcodeWriter::writeModuleLevelReferences(
   NameVals.clear();
 }
 
+// Current version for the summary.
+// This is bumped whenever we introduce changes in the way some record are
+// interpreted, like flags for instance.
+static const uint64_t INDEX_VERSION = 1;
+
 /// Emit the per-module summary section alongside the rest of
 /// the module's bitcode.
 void ModuleBitcodeWriter::writePerModuleGlobalValueSummary() {
@@ -3078,6 +3083,8 @@ void ModuleBitcodeWriter::writePerModuleGlobalValueSummary() {
 
   Stream.EnterSubblock(bitc::GLOBALVAL_SUMMARY_BLOCK_ID, 3);
 
+  Stream.EmitRecord(bitc::FS_VERSION, ArrayRef<uint64_t>{INDEX_VERSION});
+
   // Abbrev for FS_PERMODULE.
   BitCodeAbbrev *Abbv = new BitCodeAbbrev();
   Abbv->Add(BitCodeAbbrevOp(bitc::FS_PERMODULE));
@@ -3162,6 +3169,7 @@ void ModuleBitcodeWriter::writePerModuleGlobalValueSummary() {
 /// Emit the combined summary section into the combined index file.
 void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   Stream.EnterSubblock(bitc::GLOBALVAL_SUMMARY_BLOCK_ID, 3);
+  Stream.EmitRecord(bitc::FS_VERSION, ArrayRef<uint64_t>{INDEX_VERSION});
 
   // Abbrev for FS_COMBINED.
   BitCodeAbbrev *Abbv = new BitCodeAbbrev();
diff --git a/test/Bitcode/summary_version.ll b/test/Bitcode/summary_version.ll
new file mode 100644
index 00000000000..718a0ab9bd7
--- /dev/null
+++ b/test/Bitcode/summary_version.ll
@@ -0,0 +1,12 @@
+; Check summary versioning
+; RUN: opt  -module-summary  %s -o - | llvm-bcanalyzer -dump | FileCheck %s
+
+; CHECK: <GLOBALVAL_SUMMARY_BLOCK
+; CHECK: <VERSION op0=1/>
+
+
+
+; Need a function for the summary to be populated.
+define void @foo() {
+    ret void
+}
diff --git a/test/Bitcode/thinlto-alias.ll b/test/Bitcode/thinlto-alias.ll
index 7fe6d43ca48..56a01ec0553 100644
--- a/test/Bitcode/thinlto-alias.ll
+++ b/test/Bitcode/thinlto-alias.ll
@@ -6,6 +6,7 @@
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
+; CHECK-NEXT:    <VERSION
 ; See if the call to func is registered, using the expected callsite count
 ; and value id matching the subsequent value symbol table.
 ; CHECK-NEXT:    <PERMODULE {{.*}} op4=[[FUNCID:[0-9]+]] op5=1/>
@@ -17,6 +18,7 @@
 ; CHECK-NEXT:  </VALUE_SYMTAB>
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
+; COMBINED-NEXT:    <VERSION
 ; See if the call to analias is registered, using the expected callsite count
 ; and value id matching the subsequent value symbol table.
 ; COMBINED-NEXT:    <COMBINED {{.*}} op4=[[ALIASID:[0-9]+]] op5=1/>
diff --git a/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll b/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll
index dc9460849e7..7bf91a541a7 100644
--- a/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll
+++ b/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll
@@ -6,6 +6,7 @@
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
+; CHECK-NEXT:    <VERSION
 ; See if the call to func is registered, using the expected callsite count
 ; and profile count, with value id matching the subsequent value symbol table.
 ; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op4=[[FUNCID:[0-9]+]] op5=1 op6=1/>
@@ -17,6 +18,7 @@
 ; CHECK-NEXT:  </VALUE_SYMTAB>
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
+; COMBINED-NEXT:    <VERSION
 ; COMBINED-NEXT:    <COMBINED
 ; See if the call to func is registered, using the expected callsite count
 ; and profile count, with value id matching the subsequent value symbol table.
diff --git a/test/Bitcode/thinlto-function-summary-callgraph.ll b/test/Bitcode/thinlto-function-summary-callgraph.ll
index e8533dbc055..878d39391d7 100644
--- a/test/Bitcode/thinlto-function-summary-callgraph.ll
+++ b/test/Bitcode/thinlto-function-summary-callgraph.ll
@@ -6,6 +6,7 @@
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
+; CHECK-NEXT:    <VERSION
 ; See if the call to func is registered, using the expected callsite count
 ; and value id matching the subsequent value symbol table.
 ; CHECK-NEXT:    <PERMODULE {{.*}} op4=[[FUNCID:[0-9]+]] op5=1/>
@@ -17,6 +18,7 @@
 ; CHECK-NEXT:  </VALUE_SYMTAB>
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
+; COMBINED-NEXT:    <VERSION
 ; COMBINED-NEXT:    <COMBINED
 ; See if the call to func is registered, using the expected callsite count
 ; and value id matching the subsequent value symbol table.
diff --git a/test/Bitcode/thinlto-function-summary-originalnames.ll b/test/Bitcode/thinlto-function-summary-originalnames.ll
index 50c0a864e4e..26cafeadd85 100644
--- a/test/Bitcode/thinlto-function-summary-originalnames.ll
+++ b/test/Bitcode/thinlto-function-summary-originalnames.ll
@@ -4,6 +4,7 @@
 ; RUN: llvm-bcanalyzer -dump %t.index.bc | FileCheck %s --check-prefix=COMBINED
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
+; COMBINED-NEXT:    <VERSION
 ; COMBINED-DAG:    <COMBINED
 ; COMBINED-DAG:    <COMBINED_ORIGINAL_NAME op0=6699318081062747564/>
 ; COMBINED-DAG:    <COMBINED_GLOBALVAR_INIT_REFS
diff --git a/test/Bitcode/thinlto-function-summary.ll b/test/Bitcode/thinlto-function-summary.ll
index 639b68df1df..8b18f07bdeb 100644
--- a/test/Bitcode/thinlto-function-summary.ll
+++ b/test/Bitcode/thinlto-function-summary.ll
@@ -5,6 +5,7 @@
 ; same in the ValueSumbolTable, to ensure the ordering is stable.
 ; Also check the linkage field on the summary entries.
 ; BC: <GLOBALVAL_SUMMARY_BLOCK
+; BC-NEXT: <VERSION
 ; BC-NEXT: <PERMODULE {{.*}} op0=1 op1=0
 ; BC-NEXT: <PERMODULE {{.*}} op0=2 op1=0
 ; BC-NEXT: <PERMODULE {{.*}} op0=3 op1=3
diff --git a/test/tools/llvm-lto/thinlto.ll b/test/tools/llvm-lto/thinlto.ll
index b41561841cc..ee00da238c2 100644
--- a/test/tools/llvm-lto/thinlto.ll
+++ b/test/tools/llvm-lto/thinlto.ll
@@ -10,6 +10,7 @@
 ; COMBINED-NEXT: <ENTRY {{.*}} record string = '{{.*}}thinlto.ll.tmp{{.*}}.o'
 ; COMBINED-NEXT: </MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <GLOBALVAL_SUMMARY_BLOCK
+; COMBINED-NEXT: <VERSION
 ; COMBINED-NEXT: <COMBINED
 ; COMBINED-NEXT: <COMBINED
 ; COMBINED-NEXT: </GLOBALVAL_SUMMARY_BLOCK
diff --git a/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp b/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
index 0ce83c72f24..de0bf8ceda0 100644
--- a/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
+++ b/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
@@ -309,6 +309,7 @@ static const char *GetCodeName(unsigned CodeID, unsigned BlockID,
       STRINGIFY_CODE(FS, ALIAS)
       STRINGIFY_CODE(FS, COMBINED_ALIAS)
       STRINGIFY_CODE(FS, COMBINED_ORIGINAL_NAME)
+      STRINGIFY_CODE(FS, VERSION)
     }
   case bitc::METADATA_ATTACHMENT_ID:
     switch(CodeID) {