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
@@ -1075,7 +1075,12 @@
     return Tys[D.getOverloadArgNumber()];
   case IITDescriptor::ScalableVecArgument: {
     auto *Ty = cast<VectorType>(DecodeFixedType(Infos, Tys, Context));
-    return VectorType::get(Ty->getElementType(), {Ty->getNumElements(), true});
+    if (isa<ScalableVectorType>(Ty))
+      return Ty;
+    // FIXME: Explicit conversion from fixed to scalable vector. Can/should this
+    // happen?
+    return ScalableVectorType::get(Ty->getElementType(),
+                                   Ty->getElementCount().Min);
   }
   }
   llvm_unreachable("unhandled");