diff --git a/llvm/include/llvm/ADT/BitVector.h b/llvm/include/llvm/ADT/BitVector.h
--- a/llvm/include/llvm/ADT/BitVector.h
+++ b/llvm/include/llvm/ADT/BitVector.h
@@ -79,7 +79,7 @@
   static_assert(BITWORD_SIZE == 64 || BITWORD_SIZE == 32,
                 "Unsupported word size");
 
-  using Storage = std::vector<BitWord>;
+  using Storage = SmallVector<BitWord>;
 
   Storage Bits;  // Actual bits.
   unsigned Size; // Size of bitvector in bits.