diff --git a/llvm/include/llvm/ADT/PackedVector.h b/llvm/include/llvm/ADT/PackedVector.h
index 09c20e39d1552..57e41979b4ce2 100644
--- a/llvm/include/llvm/ADT/PackedVector.h
+++ b/llvm/include/llvm/ADT/PackedVector.h
@@ -29,6 +29,8 @@ namespace llvm {
 /// an assertion.
 template <typename T, unsigned BitNum, typename BitVectorTy = BitVector>
 class PackedVector {
+  static_assert(BitNum > 0, "BitNum must be > 0");
+
   BitVectorTy Bits;
   // Keep track of the number of elements on our own.
   // We always maintain Bits.size() == NumElements * BitNum.
@@ -133,9 +135,6 @@ class PackedVector {
   BitVectorTy &raw_bits() { return Bits; }
 };
 
-// Leave BitNum=0 undefined.
-template <typename T> class PackedVector<T, 0>;
-
 } // end namespace llvm
 
 #endif // LLVM_ADT_PACKEDVECTOR_H