diff --git a/include/llvm/ADT/BitVector.h b/include/llvm/ADT/BitVector.h
index a6ae1ac80d5..03789aa4ffb 100644
--- a/include/llvm/ADT/BitVector.h
+++ b/include/llvm/ADT/BitVector.h
@@ -101,7 +101,12 @@ public:
   unsigned count() const {
     unsigned NumBits = 0;
     for (unsigned i = 0; i < NumBitWords(size()); ++i)
-      NumBits = CountPopulation_32(Bits[i]);
+      if (sizeof(BitWord) == 4)
+        NumBits += CountPopulation_32(Bits[i]);
+      else if (sizeof(BitWord) == 8)
+        NumBits += CountPopulation_64(Bits[i]);
+      else
+        assert(0 && "Unsupported!")
     return NumBits;
   }