diff --git a/lib/FuzzMutate/Operations.cpp b/lib/FuzzMutate/Operations.cpp
index d59b3ccbe50..a37fd5454dd 100644
--- a/lib/FuzzMutate/Operations.cpp
+++ b/lib/FuzzMutate/Operations.cpp
@@ -302,7 +302,7 @@ static SourcePred validShuffleVectorIndex() {
     return ShuffleVectorInst::isValidOperands(Cur[0], Cur[1], V);
   };
   auto Make = [](ArrayRef<Value *> Cur, ArrayRef<Type *> Ts) {
-    auto *FirstTy = cast<VectorType>(Cur[0]->getType());
+    auto *FirstTy = cast<FixedVectorType>(Cur[0]->getType());
     auto *Int32Ty = Type::getInt32Ty(Cur[0]->getContext());
     // TODO: It's straighforward to make up reasonable values, but listing them
     // exhaustively would be insane. Come up with a couple of sensible ones.