diff --git a/include/llvm/ADT/BitVector.h b/include/llvm/ADT/BitVector.h
index b9f2d833226..3a86b0d3436 100644
--- a/include/llvm/ADT/BitVector.h
+++ b/include/llvm/ADT/BitVector.h
@@ -329,7 +329,8 @@ public:
     Size = RHS.size();
     unsigned RHSWords = NumBitWords(Size);
     if (Size <= Capacity * BITWORD_SIZE) {
-      std::copy(RHS.Bits, &RHS.Bits[RHSWords], Bits);
+      if (Size)
+        std::copy(RHS.Bits, &RHS.Bits[RHSWords], Bits);
       clear_unused_bits();
       return *this;
     }