diff --git a/velox/vector/VectorTypeUtils.h b/velox/vector/VectorTypeUtils.h
index ca6a6b3cef13..b23316db5085 100644
--- a/velox/vector/VectorTypeUtils.h
+++ b/velox/vector/VectorTypeUtils.h
@@ -85,6 +85,11 @@ struct TypeToFlatVector {
   using type = typename KindToFlatVector<SimpleTypeTrait<T>::typeKind>::type;
 };
 
+// Generic's, by design, do not have any compile time type information, so it is
+// impossible to determine what sort of Vector would hold values for this type.
+// To work around this, we just return BaseVector, since any Vector class can be
+// safely casted to BaseVector, and it is consistent with classes specialized
+// for the Generic type, like the VectorWriter.
 template <typename T, bool comparable, bool orderable>
 struct TypeToFlatVector<Generic<T, comparable, orderable>> {
   using type = BaseVector;