diff --git a/llvm/include/llvm/Support/YAMLTraits.h b/llvm/include/llvm/Support/YAMLTraits.h
--- a/llvm/include/llvm/Support/YAMLTraits.h
+++ b/llvm/include/llvm/Support/YAMLTraits.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_SUPPORT_YAMLTRAITS_H
 #define LLVM_SUPPORT_YAMLTRAITS_H
 
+#include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
@@ -1519,7 +1520,7 @@
   std::error_code                     EC;
   BumpPtrAllocator                    StringAllocator;
   document_iterator                   DocIterator;
-  std::vector<bool>                   BitValuesUsed;
+  llvm::BitVector                     BitValuesUsed;
   HNode *CurrentNode = nullptr;
   bool                                ScalarMatchFound = false;
   bool AllowUnknownKeys = false;
diff --git a/llvm/lib/Support/YAMLTraits.cpp b/llvm/lib/Support/YAMLTraits.cpp
--- a/llvm/lib/Support/YAMLTraits.cpp
+++ b/llvm/lib/Support/YAMLTraits.cpp
@@ -298,7 +298,7 @@
 bool Input::beginBitSetScalar(bool &DoClear) {
   BitValuesUsed.clear();
   if (SequenceHNode *SQ = dyn_cast<SequenceHNode>(CurrentNode)) {
-    BitValuesUsed.insert(BitValuesUsed.begin(), SQ->Entries.size(), false);
+    BitValuesUsed.resize(SQ->Entries.size(), false);
   } else {
     setError(CurrentNode, "expected sequence of bit values");
   }