diff --git a/README.md b/README.md
index be05249..dbecf22 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 Metaprogramming for Ethereum Smart Contracts expressed in Scala's Type System.
 
-- Unlock Smart Contracts **adoption with JVM**-based language: code them _from_ Scala or _in_ Scala
+- Unlock Smart Contracts **adoption with a JVM**-based language: code them _from_ Scala or _in_ Scala
 - Smart Contracts code generator is itself **a strictly typed program**
 - Write a Contract using structs and definitions of **Crotalinae DSL**, and if it compiles, you're **safe**
 - **Export** Smart Contract in [Vyper](https://github.com/ethereum/vyper) as a single plaintext and check it visually if needed
diff --git a/core/src/main/scala/fluence/hackethberlin/types/ProductType.scala b/core/src/main/scala/fluence/hackethberlin/types/ProductType.scala
index d497df5..157e5fd 100644
--- a/core/src/main/scala/fluence/hackethberlin/types/ProductType.scala
+++ b/core/src/main/scala/fluence/hackethberlin/types/ProductType.scala
@@ -5,10 +5,10 @@ import fluence.hackethberlin.{Expr, FuncDef, InlineExpr}
 import shapeless._
 import shapeless.ops.record.Selector
 
-class ProductType[D <: HList](dataDef: D, dv: DataVyper[D]) extends Type {
+class ProductType[D <: HList](dataDef: D, refPrefix: String, dv: DataVyper[D]) extends Type {
 
   def ref[T <: Symbol, V <: Type](k: Witness.Aux[T])(implicit selector: Selector.Aux[D, T, V]): Expr.Ref[V] =
-    Expr.Ref[V](k.value.name, selector(dataDef))
+    Expr.Ref[V](refPrefix + k.value.name, selector(dataDef))
 
   // type in type definition somewhere
   override def toVyper: String =
@@ -35,7 +35,10 @@ class ProductType[D <: HList](dataDef: D, dv: DataVyper[D]) extends Type {
 object ProductType {
 
   def apply[D <: HList](dataDef: D)(implicit dv: DataVyper[D]): ProductType[D] =
-    new ProductType[D](dataDef, dv)
+    new ProductType[D](dataDef, "", dv)
+
+  def self[D <: HList](dataDef: D)(implicit dv: DataVyper[D]): ProductType[D] =
+    new ProductType[D](dataDef, "self.", dv)
 
   def hNil: ProductType[HNil] = ProductType(HNil)
 }
diff --git a/src/main/scala/fluence/MakeVyperApp.scala b/src/main/scala/fluence/MakeVyperApp.scala
index e12af31..8f38a11 100644
--- a/src/main/scala/fluence/MakeVyperApp.scala
+++ b/src/main/scala/fluence/MakeVyperApp.scala
@@ -87,7 +87,7 @@ object Auction extends App {
   val `msg.sender` = predef.ref(Symbol("msg.sender"))
   val `True` = predef.ref('True)
 
-  val data = ProductType(
+  val data = ProductType.self(
     ('beneficiary ->> public(address)) ::
       ('auction_start ->> public(timestamp)) ::
       ('auction_end ->> public(timestamp)) ::