diff --git a/project.scala b/project.scala
index 91af199..5575473 100644
--- a/project.scala
+++ b/project.scala
@@ -1,6 +1,6 @@
 //> using scala 3.9.0-RC6
 
-//> using dep com.halotukozak::made::0.3.1
+//> using dep com.halotukozak::made::0.4.0
 
 //> using test.dep org.scalameta::munit::1.3.5
 //> using test.dep org.scalameta::munit-scalacheck::1.3.0
diff --git a/src/mcodec/Derivation.scala b/src/mcodec/Derivation.scala
index 4dafc2d..3427c33 100644
--- a/src/mcodec/Derivation.scala
+++ b/src/mcodec/Derivation.scala
@@ -24,8 +24,8 @@ trait Derivation:
     compiletime.constValueTuple[m.ElemLabels].toArrayOf[String],
     compiletime.summonAll[Tuple.Map[m.ElemTypes, MCodec]].toArrayOf[MCodec[Any]](using containsOnly.refl),
     m.elems
-      .mapAs[MadeFieldElem][[e] =>> Option[Any]]([e <: MadeFieldElem] => elem => elem.default)
-      .toArrayOf[Option[Any]],
+      .mapAs[MadeFieldElem][[e] =>> Any | NotExists]([e <: MadeFieldElem] => elem => elem.default)
+      .toArrayOf[Any | NotExists],
     m.elems.hasAnnotations[optionalParam].toArrayOf[Boolean],
     isOptionFlags[m.ElemTypes].toArray,
     m.elems.hasAnnotations[halotukozak.mcodec.annotation.transientDefault].toArrayOf[Boolean],
diff --git a/src/mcodec/DerivedCodecs.scala b/src/mcodec/DerivedCodecs.scala
index 5743fd7..9c4ae00 100644
--- a/src/mcodec/DerivedCodecs.scala
+++ b/src/mcodec/DerivedCodecs.scala
@@ -1,5 +1,7 @@
 package halotukozak.mcodec
 
+import halotukozak.made.NotExists
+
 final class Deferred[T] extends MCodec[T]:
   private[mcodec] var underlying: MCodec[T] | Null = compiletime.uninitialized
 
@@ -15,7 +17,7 @@ final class ProductCodec[T](
   typeName: String,
   labels: Array[String],
   childCodecsByName: => Array[MCodec[Any]],
-  defaults: Array[Option[Any]],
+  defaults: Array[Any | NotExists],
   optionalFlags: Array[Boolean],
   isOption: Array[Boolean],
   transientDefaultFlags: Array[Boolean],
@@ -36,7 +38,7 @@ final class ProductCodec[T](
   // `forced` (the IgnoreTransientDefaults marker) disables the transient-default omission.
   private def isOmitted(i: Int, p: Product, forced: Boolean): Boolean =
     ((optionalFlags(i) || isOption(i)) && (p.productElement(i) == None)) ||
-      (!forced && transientDefaultFlags(i) && defaults(i).contains(p.productElement(i)))
+      (!forced && transientDefaultFlags(i) && defaults(i) != null && defaults(i) == p.productElement(i))
 
   private[mcodec] def writtenFieldCount(value: T, forced: Boolean): Int =
     val p = value.asInstanceOf[Product]
@@ -88,10 +90,10 @@ final class ProductCodec[T](
     while i < labels.length do
       if !seen(i) then
         values(i) = defaults(i) match
-          case Some(d) => d
-          case None =>
+          case NotExists =>
             if optionalFlags(i) || isOption(i) then None
             else throw new MissingField(s"missing field: ${labels(i)}")
+          case d => d
       i += 1
     fromArray(values)
   catch case rf: ReadFailure => throw rf.withRootType(typeName)
diff --git a/test/mcodec/MirrorAdapterTest.scala b/test/mcodec/MirrorAdapterTest.scala
index edcc8ad..9e0148a 100644
--- a/test/mcodec/MirrorAdapterTest.scala
+++ b/test/mcodec/MirrorAdapterTest.scala
@@ -9,7 +9,6 @@ class MirrorAdapterTest extends munit.FunSuite:
   test("Made.derived resolves in-project and the enriched mirror is readable"):
     val m = Made.derived[User]
     val (nameElem, ageElem) = m.elems
-    // Made 0.1.1: `Label` is a type member, read via constValue.
     assertEquals(compiletime.constValue[nameElem.Label], "user_name")
-    assertEquals(nameElem.default, None)
-    assertEquals(ageElem.default, Some(18))
+    assertEquals(nameElem.default, NotExists)
+    assertEquals(ageElem.default, 18)