diff --git a/core/src/fr/hammons/slinc/Mem.scala b/core/src/fr/hammons/slinc/Mem.scala
index b2da4e9..94e436c 100644
--- a/core/src/fr/hammons/slinc/Mem.scala
+++ b/core/src/fr/hammons/slinc/Mem.scala
@@ -7,6 +7,7 @@ trait Mem:
   def asBase: Object
   def asAddress: Object
   def asVarArgs: VarArgs
+  def copyFrom(other: Mem): Unit
 
   def writeFloat(v: Float, offset: Bytes): Unit
   def writeLong(v: Long, offset: Bytes): Unit
diff --git a/core/src/fr/hammons/slinc/TypeDescriptor.scala b/core/src/fr/hammons/slinc/TypeDescriptor.scala
index d6630a6..ce1d46d 100644
--- a/core/src/fr/hammons/slinc/TypeDescriptor.scala
+++ b/core/src/fr/hammons/slinc/TypeDescriptor.scala
@@ -201,11 +201,12 @@ case class CUnionDescriptor(possibleTypes: Set[TypeDescriptor])
   type Inner = CUnion[? <: NonEmptyTuple]
 
   override val reader: (ReadWriteModule, DescriptorModule) ?=> Reader[Inner] =
-    ???
+    summon[ReadWriteModule].unionReader(this)
 
   override val returnTransition
       : (TransitionModule, ReadWriteModule) ?=> ReturnTransition[Inner] = obj =>
-    summon[TransitionModule].cUnionReturn(this, obj).asInstanceOf[Inner]
+    summon[ReadWriteModule]
+      .unionReader(this)(summon[TransitionModule].memReturn(obj), Bytes(0))
 
   override val argumentTransition
       : (TransitionModule, ReadWriteModule, Allocator) ?=> ArgumentTransition[
@@ -213,4 +214,4 @@ case class CUnionDescriptor(possibleTypes: Set[TypeDescriptor])
       ] = (i: Inner) => i.mem.asBase
 
   override val writer: (ReadWriteModule, DescriptorModule) ?=> Writer[Inner] =
-    ???
+    summon[ReadWriteModule].unionWriter(this)
diff --git a/core/src/fr/hammons/slinc/modules/ReadWriteModule.scala b/core/src/fr/hammons/slinc/modules/ReadWriteModule.scala
index 7f08445..c232b36 100644
--- a/core/src/fr/hammons/slinc/modules/ReadWriteModule.scala
+++ b/core/src/fr/hammons/slinc/modules/ReadWriteModule.scala
@@ -3,6 +3,7 @@ package fr.hammons.slinc.modules
 import fr.hammons.slinc.*
 import java.lang.invoke.MethodHandle
 import scala.reflect.ClassTag
+import scala.NonEmptyTuple
 
 type Reader[A] = (Mem, Bytes) => A
 type Writer[A] = (Mem, Bytes, A) => Unit
@@ -27,6 +28,8 @@ trait ReadWriteModule:
 
   val memReader: Reader[Mem]
   val memWriter: Writer[Mem]
+  def unionReader(td: TypeDescriptor): Reader[CUnion[? <: NonEmptyTuple]]
+  def unionWriter(td: TypeDescriptor): Writer[CUnion[? <: NonEmptyTuple]]
 
   def write(
       memory: Mem,
diff --git a/core/src/fr/hammons/slinc/modules/TransitionModule.scala b/core/src/fr/hammons/slinc/modules/TransitionModule.scala
index 21545a1..20c488b 100644
--- a/core/src/fr/hammons/slinc/modules/TransitionModule.scala
+++ b/core/src/fr/hammons/slinc/modules/TransitionModule.scala
@@ -44,8 +44,6 @@ trait TransitionModule:
 
   def memReturn(value: Object): Mem
 
-  def cUnionReturn(td: TypeDescriptor, value: Object): CUnion[?]
-
   def functionArgument[A](td: TypeDescriptor, value: Object): A =
     methodReturn[A](td, value)
 
diff --git a/core/test/resources/native/test.c b/core/test/resources/native/test.c
index 191cadc..9721d26 100644
--- a/core/test/resources/native/test.c
+++ b/core/test/resources/native/test.c
@@ -123,4 +123,19 @@ EXPORTED union_b_issue_176 i176_test(union_a_issue_176 a, char is_left) {
   }
 
   return b;
-}
\ No newline at end of file
+}
+
+typedef struct {
+  union {
+    long x;
+    double y;
+  } my_union;
+} struct_issue_175;
+EXPORTED struct_issue_175 i175_test(struct_issue_175 a, char left) {
+  if(left) {
+    a.my_union.x = a.my_union.x * 2;
+  } else {
+    a.my_union.y = a.my_union.y / 2;
+  }
+  return a;
+}
diff --git a/core/test/src/fr/hammons/slinc/BindingSpec.scala b/core/test/src/fr/hammons/slinc/BindingSpec.scala
index 0092ea5..ef8a049 100644
--- a/core/test/src/fr/hammons/slinc/BindingSpec.scala
+++ b/core/test/src/fr/hammons/slinc/BindingSpec.scala
@@ -22,6 +22,7 @@ trait BindingSpec(val slinc: Slinc) extends ScalaCheckSuite:
   case class I36Outer(inner: Ptr[I36Inner]) derives Struct
 
   case class I30Struct(list: Ptr[VarArgs]) derives Struct
+  case class I175_Struct(union: CUnion[(CInt, CDouble)]) derives Struct
 
   @NeedsResource("test")
   trait TestLib derives FSet:
@@ -53,6 +54,11 @@ trait BindingSpec(val slinc: Slinc) extends ScalaCheckSuite:
         is_left: CChar
     ): CUnion[(CLong, CDouble)]
 
+    def i175_test(
+        input: I175_Struct,
+        left: CChar
+    ): I175_Struct
+
   test("int_identity") {
     val test = FSet.instance[TestLib]
 
@@ -162,3 +168,21 @@ trait BindingSpec(val slinc: Slinc) extends ScalaCheckSuite:
           union.set(int)
           val res = test.i176_test(union, 0).get[CLong]
           assertEquals(res, CLong(int))
+
+  property(
+    "issue 175 - can send and receive structs with union types to C functions"
+  ):
+      val test = FSet.instance[TestLib]
+      forAll: (int: CInt, double: CDouble, left: Boolean) =>
+        val union = CUnion[(CInt, CDouble)]
+        if left then
+          union.set(int)
+          val res = test.i175_test(I175_Struct(union), 1)
+          assertEquals(
+            res.union.get[CInt],
+            int * 2
+          )
+        else
+          union.set(double)
+          val res = test.i175_test(I175_Struct(union), 0)
+          assertEquals(res.union.get[CDouble], double / 2)
diff --git a/core/test/src/fr/hammons/slinc/TransferSpec.scala b/core/test/src/fr/hammons/slinc/TransferSpec.scala
index 40f2d8f..5f6d4af 100644
--- a/core/test/src/fr/hammons/slinc/TransferSpec.scala
+++ b/core/test/src/fr/hammons/slinc/TransferSpec.scala
@@ -26,6 +26,8 @@ trait TransferSpec[ThreadException <: Throwable](val slinc: Slinc)(using
 
   case class E(list: VarArgs) derives Struct
 
+  case class F(u: CUnion[(CInt, CFloat)]) derives Struct
+
   test("can read and write jvm ints") {
     Scope.global {
       val mem = Ptr.blank[Int]
@@ -331,3 +333,23 @@ trait TransferSpec[ThreadException <: Throwable](val slinc: Slinc)(using
 
       assertEquals(deallocated, false)
       assertEquals(union.get[CInt], 0)
+
+  property("can create F ptrs"):
+      val union = CUnion[(CInt, CFloat)]
+      forAll: (a: CInt, b: CFloat, left: Boolean) =>
+        if left then
+          union.set(a)
+          val fReturn = Scope.confined {
+            val f = Ptr.copy(F(union))
+            !f
+          }
+
+          assertEquals(fReturn.u.get[CInt], union.get[CInt])
+        else
+          union.set(b)
+          val fReturn = Scope.confined {
+            val f = Ptr.copy(F(union))
+            !f
+          }
+
+          assertEquals(fReturn.u.get[CFloat], union.get[CFloat])
diff --git a/j17/src/fr/hammons/slinc/Allocator17.scala b/j17/src/fr/hammons/slinc/Allocator17.scala
index e68eafb..9d93faa 100644
--- a/j17/src/fr/hammons/slinc/Allocator17.scala
+++ b/j17/src/fr/hammons/slinc/Allocator17.scala
@@ -11,7 +11,6 @@ import jdk.incubator.foreign.{
 }, CLinker.{C_POINTER, C_INT, C_LONG_LONG, C_DOUBLE, VaList}
 import fr.hammons.slinc.modules.{descriptorModule17, transitionModule17}
 import fr.hammons.slinc.modules.LinkageModule17
-import java.lang.ref.Cleaner
 
 class Allocator17(
     segmentAllocator: SegmentAllocator,
diff --git a/j17/src/fr/hammons/slinc/Mem17.scala b/j17/src/fr/hammons/slinc/Mem17.scala
index 4ba6403..7149630 100644
--- a/j17/src/fr/hammons/slinc/Mem17.scala
+++ b/j17/src/fr/hammons/slinc/Mem17.scala
@@ -18,6 +18,10 @@ class Mem17(private[slinc] val mem: MemorySegment) extends Mem:
     VaList.ofAddress(mem.address().nn).nn
   )
 
+  override def copyFrom(other: Mem): Unit =
+    other match
+      case oMem: Mem17 => mem.copyFrom(oMem.mem)
+
   override def readLong(offset: Bytes): Long =
     MemoryAccess.getLongAtOffset(mem, offset.toLong)
 
diff --git a/j17/src/fr/hammons/slinc/Scope17.scala b/j17/src/fr/hammons/slinc/Scope17.scala
index 8c9d5fe..8c134f3 100644
--- a/j17/src/fr/hammons/slinc/Scope17.scala
+++ b/j17/src/fr/hammons/slinc/Scope17.scala
@@ -1,11 +1,10 @@
 package fr.hammons.slinc
 
-import jdk.incubator.foreign.CLinker
 import jdk.incubator.foreign.ResourceScope
 import jdk.incubator.foreign.SegmentAllocator
 import jdk.incubator.foreign.MemoryAddress
 
-class Scope17(linker: CLinker) extends ScopeI.PlatformSpecific:
+object Scope17 extends ScopeI.PlatformSpecific:
   private val baseNull = Ptr[Nothing](
     Mem17(MemoryAddress.NULL.nn.asSegment(1, ResourceScope.globalScope).nn),
     Bytes(0)
@@ -17,14 +16,14 @@ class Scope17(linker: CLinker) extends ScopeI.PlatformSpecific:
     def apply[A](fn: (Allocator) ?=> A): A =
       val rs = ResourceScope.globalScope().nn
       given Allocator =
-        Allocator17(SegmentAllocator.arenaAllocator(rs).nn, rs, linker)
+        Allocator17(SegmentAllocator.arenaAllocator(rs).nn, rs, Slinc17.linker)
       fn
 
   def createConfinedScope: ConfinedScope = new ConfinedScope:
     def apply[A](fn: Allocator ?=> A): A =
       val rs = ResourceScope.newConfinedScope().nn
       given Allocator =
-        Allocator17(SegmentAllocator.arenaAllocator(rs).nn, rs, linker)
+        Allocator17(SegmentAllocator.arenaAllocator(rs).nn, rs, Slinc17.linker)
       val res = fn
       rs.close()
       res
@@ -33,7 +32,7 @@ class Scope17(linker: CLinker) extends ScopeI.PlatformSpecific:
     def apply[A](fn: Allocator ?=> A): A =
       val rs = ResourceScope.newSharedScope().nn
       given Allocator =
-        Allocator17(SegmentAllocator.arenaAllocator(rs).nn, rs, linker)
+        Allocator17(SegmentAllocator.arenaAllocator(rs).nn, rs, Slinc17.linker)
       val res = fn
       rs.close()
       res
@@ -46,7 +45,7 @@ class Scope17(linker: CLinker) extends ScopeI.PlatformSpecific:
       given Allocator = Allocator17(
         segmentAllocator,
         ResourceScope.globalScope().nn,
-        linker
+        Slinc17.linker
       )
       val res = fn
       allocator.reset()
@@ -55,5 +54,5 @@ class Scope17(linker: CLinker) extends ScopeI.PlatformSpecific:
   def createInferredScope: InferredScope = new InferredScope:
     def apply[A](fn: Allocator ?=> A): A =
       val scope = ResourceScope.newSharedScope().nn
-      given Allocator = InferredAllocator17(scope, linker)
+      given Allocator = InferredAllocator17(scope, Slinc17.linker)
       fn
diff --git a/j17/src/fr/hammons/slinc/Slinc17.scala b/j17/src/fr/hammons/slinc/Slinc17.scala
index 37da9c0..83ac9b1 100644
--- a/j17/src/fr/hammons/slinc/Slinc17.scala
+++ b/j17/src/fr/hammons/slinc/Slinc17.scala
@@ -9,7 +9,7 @@ import fr.hammons.slinc.modules.{
 }
 import fr.hammons.slinc.modules.given
 
-class Slinc17(_jitManager: JitManager, linker: CLinker)(using
+class Slinc17(_jitManager: JitManager)(using
     val dm: DescriptorModule,
     val tm: TransitionModule,
     val rwm: ReadWriteModule,
@@ -17,13 +17,13 @@ class Slinc17(_jitManager: JitManager, linker: CLinker)(using
 ) extends Slinc:
   val version: Int = 17
   protected def jitManager = _jitManager
-  protected def scopePlatformSpecific = Scope17(linker)
+  protected def scopePlatformSpecific = Scope17
 
 @SlincImpl(17)
 object Slinc17:
-  private val compiler =
+  private lazy val compiler =
     scala.quoted.staging.Compiler.make(getClass().getClassLoader().nn)
-  private[slinc] val linker = CLinker.getInstance().nn
-  val default = Slinc17(JitManagerImpl(compiler), linker)
-  val noJit = Slinc17(NoJitManager, linker)
-  val immediateJit = Slinc17(InstantJitManager(compiler), linker)
+  private[slinc] lazy val linker = CLinker.getInstance().nn
+  val default = Slinc17(JitManagerImpl(compiler))
+  val noJit = Slinc17(NoJitManager)
+  val immediateJit = Slinc17(InstantJitManager(compiler))
diff --git a/j17/src/fr/hammons/slinc/modules/LinkageModule17.scala b/j17/src/fr/hammons/slinc/modules/LinkageModule17.scala
index a873693..dc524cf 100644
--- a/j17/src/fr/hammons/slinc/modules/LinkageModule17.scala
+++ b/j17/src/fr/hammons/slinc/modules/LinkageModule17.scala
@@ -9,10 +9,8 @@ import java.lang.invoke.MethodType
 object LinkageModule17 extends LinkageModule:
   import descriptorModule17.*
   override type CSymbol = Addressable
-  private val linker = CLinker.getInstance().nn
   private val lookup = CLinker.systemLookup().nn
   private val lookupLoader = SymbolLookup.loaderLookup().nn
-  private val ts = Scope17(linker)
 
   override def defaultLookup(name: String): Option[CSymbol] =
     lookup.lookup(name).nn.toScala
@@ -59,7 +57,7 @@ object LinkageModule17 extends LinkageModule:
         .toSeq
     )
 
-    linker.downcallHandle(mt, fd).nn
+    Slinc17.linker.downcallHandle(mt, fd).nn
   end getDowncall
 
-  lazy val tempScope: Scope = ts.createTempScope
+  lazy val tempScope: Scope = Scope17.createTempScope
diff --git a/j17/src/fr/hammons/slinc/modules/ReadWriteModule17.scala b/j17/src/fr/hammons/slinc/modules/ReadWriteModule17.scala
index 094ca86..127d93f 100644
--- a/j17/src/fr/hammons/slinc/modules/ReadWriteModule17.scala
+++ b/j17/src/fr/hammons/slinc/modules/ReadWriteModule17.scala
@@ -41,6 +41,22 @@ given readWriteModule17: ReadWriteModule with
 
   val memReader = (mem, offset) => mem.readAddress(offset)
 
+  def unionReader(
+      typeDescriptor: TypeDescriptor
+  ): Reader[CUnion[? <: NonEmptyTuple]] =
+    val size = descriptorModule17.sizeOf(typeDescriptor)
+    (mem, offset) =>
+      Scope17.createInferredScope(alloc ?=>
+        val newMem = alloc.allocate(typeDescriptor, 1)
+        newMem.copyFrom(mem.offset(offset).resize(size))
+
+        new CUnion(newMem)
+      )
+
+  def unionWriter(td: TypeDescriptor): Writer[CUnion[? <: NonEmptyTuple]] =
+    val size = descriptorModule17.sizeOf(td)
+    (mem, offset, value) => mem.offset(offset).resize(size).copyFrom(value.mem)
+
   arrayWriterCache
     .addOne(
       ByteDescriptor,
diff --git a/j17/src/fr/hammons/slinc/modules/TransitionModule17.scala b/j17/src/fr/hammons/slinc/modules/TransitionModule17.scala
index 227a8fe..c061e9a 100644
--- a/j17/src/fr/hammons/slinc/modules/TransitionModule17.scala
+++ b/j17/src/fr/hammons/slinc/modules/TransitionModule17.scala
@@ -5,12 +5,7 @@ import fr.hammons.slinc.TypeDescriptor
 import scala.collection.concurrent.TrieMap
 import fr.hammons.slinc.*
 
-import jdk.incubator.foreign.{
-  MemoryAddress,
-  MemorySegment,
-  ResourceScope,
-  SegmentAllocator
-}
+import jdk.incubator.foreign.{MemoryAddress, MemorySegment}
 
 given transitionModule17: TransitionModule with
 
@@ -18,13 +13,6 @@ given transitionModule17: TransitionModule with
     value.asInstanceOf[MemorySegment]
   )
 
-  override def cUnionReturn(td: TypeDescriptor, value: Object): CUnion[?] =
-    val scope = ResourceScope.newImplicitScope().nn
-    val alloc = SegmentAllocator.arenaAllocator(scope).nn
-    val segment = alloc.allocate(descriptorModule17.toMemoryLayout(td)).nn
-    segment.copyFrom(value.asInstanceOf[MemorySegment])
-    new CUnion(Mem17(segment))
-
   override def addressReturn(value: Object): Mem = Mem17(
     MemorySegment
       .globalNativeSegment()
diff --git a/j19/src/fr/hammons/slinc/Mem19.scala b/j19/src/fr/hammons/slinc/Mem19.scala
index 9df4249..6093d71 100644
--- a/j19/src/fr/hammons/slinc/Mem19.scala
+++ b/j19/src/fr/hammons/slinc/Mem19.scala
@@ -19,6 +19,9 @@ object Mem19:
 class Mem19(private[slinc] val mem: MemorySegment) extends Mem:
   import Mem19.*
 
+  override def copyFrom(other: Mem): Unit = other match
+    case oMem: Mem19 => mem.copyFrom(oMem.mem).nn
+
   override def writeByteArray(v: Array[Byte], offset: Bytes): Unit =
     mem.asSlice(offset.toLong).nn.copyFrom(MemorySegment.ofArray(v))
 
diff --git a/j19/src/fr/hammons/slinc/Scope19.scala b/j19/src/fr/hammons/slinc/Scope19.scala
index 6069b86..02fec03 100644
--- a/j19/src/fr/hammons/slinc/Scope19.scala
+++ b/j19/src/fr/hammons/slinc/Scope19.scala
@@ -1,12 +1,11 @@
 package fr.hammons.slinc
 
-import java.lang.foreign.Linker
 import java.lang.foreign.MemorySession
 import java.lang.foreign.SegmentAllocator
 import java.lang.foreign.MemorySegment
 import java.lang.foreign.MemoryAddress
 
-class Scope19(linker: Linker) extends ScopeI.PlatformSpecific:
+object Scope19 extends ScopeI.PlatformSpecific:
 
   val baseNull: Ptr[Any] = Ptr(
     Mem19(
@@ -20,7 +19,7 @@ class Scope19(linker: Linker) extends ScopeI.PlatformSpecific:
     given Allocator = Allocator19(
       TempAllocator19.localAllocator,
       MemorySession.global().nn,
-      linker
+      Slinc19.linker
     )
     def apply[A](fn: Allocator ?=> A): A =
       val res = fn
@@ -31,14 +30,14 @@ class Scope19(linker: Linker) extends ScopeI.PlatformSpecific:
     def apply[A](fn: Allocator ?=> A): A =
       val rs = MemorySession.global().nn
       given Allocator =
-        Allocator19(SegmentAllocator.newNativeArena(rs).nn, rs, linker)
+        Allocator19(SegmentAllocator.newNativeArena(rs).nn, rs, Slinc19.linker)
       fn
 
   override def createConfinedScope: ConfinedScope = new ConfinedScope:
     def apply[A](fn: Allocator ?=> A): A =
       val rs = MemorySession.openConfined().nn
       given Allocator =
-        Allocator19(SegmentAllocator.newNativeArena(rs).nn, rs, linker)
+        Allocator19(SegmentAllocator.newNativeArena(rs).nn, rs, Slinc19.linker)
       val res = fn
       rs.close()
       res
@@ -47,7 +46,7 @@ class Scope19(linker: Linker) extends ScopeI.PlatformSpecific:
     def apply[A](fn: Allocator ?=> A): A =
       val rs = MemorySession.openShared().nn
       given Allocator =
-        Allocator19(SegmentAllocator.newNativeArena(rs).nn, rs, linker)
+        Allocator19(SegmentAllocator.newNativeArena(rs).nn, rs, Slinc19.linker)
       val res = fn
       rs.close()
       res
@@ -57,5 +56,5 @@ class Scope19(linker: Linker) extends ScopeI.PlatformSpecific:
       val rs = MemorySession.openImplicit().nn
 
       given Allocator =
-        Allocator19(SegmentAllocator.newNativeArena(rs).nn, rs, linker)
+        Allocator19(SegmentAllocator.newNativeArena(rs).nn, rs, Slinc19.linker)
       fn
diff --git a/j19/src/fr/hammons/slinc/Slinc19.scala b/j19/src/fr/hammons/slinc/Slinc19.scala
index 4a1aec0..79e2b62 100644
--- a/j19/src/fr/hammons/slinc/Slinc19.scala
+++ b/j19/src/fr/hammons/slinc/Slinc19.scala
@@ -3,7 +3,7 @@ package fr.hammons.slinc
 import java.lang.foreign.Linker
 import fr.hammons.slinc.modules.{*, given}
 
-class Slinc19(_jitManager: JitManager, linker: Linker)(using
+class Slinc19(_jitManager: JitManager)(using
     val dm: DescriptorModule,
     val tm: TransitionModule,
     val rwm: ReadWriteModule,
@@ -13,13 +13,13 @@ class Slinc19(_jitManager: JitManager, linker: Linker)(using
   protected def jitManager: JitManager = _jitManager
 
   protected def scopePlatformSpecific: ScopeI.PlatformSpecific =
-    Scope19(linker)
+    Scope19
 
 @SlincImpl(19)
 object Slinc19:
   private val compiler =
     scala.quoted.staging.Compiler.make(getClass().getClassLoader().nn)
-  private[slinc] val linker = Linker.nativeLinker().nn
-  val default = Slinc19(JitManagerImpl(compiler), linker)
-  val noJit = Slinc19(NoJitManager, linker)
-  val immediateJit = Slinc19(InstantJitManager(compiler), linker)
+  private[slinc] lazy val linker = Linker.nativeLinker().nn
+  val default = Slinc19(JitManagerImpl(compiler))
+  val noJit = Slinc19(NoJitManager)
+  val immediateJit = Slinc19(InstantJitManager(compiler))
diff --git a/j19/src/fr/hammons/slinc/modules/LinkageModule19.scala b/j19/src/fr/hammons/slinc/modules/LinkageModule19.scala
index a256080..4c6d335 100644
--- a/j19/src/fr/hammons/slinc/modules/LinkageModule19.scala
+++ b/j19/src/fr/hammons/slinc/modules/LinkageModule19.scala
@@ -1,7 +1,6 @@
 package fr.hammons.slinc.modules
 
 import java.lang.invoke.MethodHandle
-import java.lang.foreign.Linker
 import java.lang.foreign.{FunctionDescriptor as JFunctionDescriptor}
 import scala.jdk.OptionConverters.*
 import java.lang.foreign.MemorySegment
@@ -12,10 +11,8 @@ import java.lang.foreign.SymbolLookup
 object LinkageModule19 extends LinkageModule:
   import descriptorModule19.*
   override type CSymbol = MemorySegment
-  private val linker = Linker.nativeLinker().nn
-  private val lookup = linker.defaultLookup().nn
+  private val lookup = Slinc19.linker.defaultLookup().nn
   private val loaderLookup = SymbolLookup.loaderLookup().nn
-  private val ts = Scope19(linker)
 
   override def defaultLookup(name: String): Option[CSymbol] =
     lookup.lookup(name).nn.toScala
@@ -57,7 +54,7 @@ object LinkageModule19 extends LinkageModule:
         .toList
     )
 
-    linker.downcallHandle(fd).nn
+    Slinc19.linker.downcallHandle(fd).nn
   end getDowncall
 
-  lazy val tempScope: Scope = ts.createTempScope
+  lazy val tempScope: Scope = Scope19.createTempScope
diff --git a/j19/src/fr/hammons/slinc/modules/ReadWriteModule19.scala b/j19/src/fr/hammons/slinc/modules/ReadWriteModule19.scala
index 5071b14..f0dd6b6 100644
--- a/j19/src/fr/hammons/slinc/modules/ReadWriteModule19.scala
+++ b/j19/src/fr/hammons/slinc/modules/ReadWriteModule19.scala
@@ -6,6 +6,24 @@ import java.lang.invoke.MethodHandle
 import scala.reflect.ClassTag
 
 private[slinc] given readWriteModule19: ReadWriteModule with
+
+  override def unionWriter(
+      td: TypeDescriptor
+  ): Writer[CUnion[? <: NonEmptyTuple]] =
+    val size = descriptorModule19.sizeOf(td)
+    (mem, offset, value) => mem.offset(offset).resize(size).copyFrom(value.mem)
+
+  override def unionReader(
+      td: TypeDescriptor
+  ): Reader[CUnion[? <: NonEmptyTuple]] =
+    val size = descriptorModule19.sizeOf(td)
+    (mem, offset) =>
+      Scope19.createInferredScope(alloc ?=>
+        val newMem = alloc.allocate(td, 1)
+        newMem.copyFrom(mem.offset(offset).resize(size))
+        new CUnion(newMem)
+      )
+
   val writerCache = DependentTrieMap[Writer]
 
   val arrayWriterCache = DependentTrieMap[[I] =>> Writer[Array[I]]]
diff --git a/j19/src/fr/hammons/slinc/modules/TransitionModule19.scala b/j19/src/fr/hammons/slinc/modules/TransitionModule19.scala
index 42956d3..29b04df 100644
--- a/j19/src/fr/hammons/slinc/modules/TransitionModule19.scala
+++ b/j19/src/fr/hammons/slinc/modules/TransitionModule19.scala
@@ -5,7 +5,6 @@ import scala.collection.concurrent.TrieMap
 import java.lang.foreign.MemorySegment
 import java.lang.foreign.MemorySession
 import java.lang.foreign.MemoryAddress
-import java.lang.foreign.SegmentAllocator
 
 given transitionModule19: TransitionModule with
 
@@ -44,14 +43,3 @@ given transitionModule19: TransitionModule with
   override def memReturn(value: Object): Mem = Mem19(
     value.asInstanceOf[MemorySegment]
   )
-
-  override def cUnionReturn(td: TypeDescriptor, value: Object): CUnion[?] =
-    val session = MemorySession.openImplicit().nn
-    val segmentAlloc = SegmentAllocator.newNativeArena(session).nn
-    val segment =
-      segmentAlloc.allocate(descriptorModule19.toMemoryLayout(td)).nn
-    new CUnion(
-      Mem19(
-        segment.copyFrom(value.asInstanceOf[MemorySegment]).nn
-      )
-    )