diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -1074,8 +1074,8 @@
     // Return the overloaded type (which determines the pointers address space)
     return Tys[D.getOverloadArgNumber()];
   case IITDescriptor::ScalableVecArgument: {
-    auto *Ty = cast<VectorType>(DecodeFixedType(Infos, Tys, Context));
-    return VectorType::get(Ty->getElementType(), {Ty->getNumElements(), true});
+    auto *Ty = cast<FixedVectorType>(DecodeFixedType(Infos, Tys, Context));
+    return ScalableVectorType::get(Ty->getElementType(), Ty->getNumElements());
   }
   }
   llvm_unreachable("unhandled");