diff --git a/include/llvm/Analysis/ScalarEvolutionExpressions.h b/include/llvm/Analysis/ScalarEvolutionExpressions.h
index 74242031edd..dd311c5508c 100644
--- a/include/llvm/Analysis/ScalarEvolutionExpressions.h
+++ b/include/llvm/Analysis/ScalarEvolutionExpressions.h
@@ -523,6 +523,8 @@ namespace llvm {
   class SCEVUnknown : public SCEV {
     friend class ScalarEvolution;
 
+    // This should be an AssertingVH, however SCEVUnknowns are allocated in a
+    // BumpPtrAllocator so their destructors are never called.
     Value *V;
     SCEVUnknown(const FoldingSetNodeIDRef ID, Value *v) :
       SCEV(ID, scUnknown), V(v) {}