diff --git a/modules/core/src/main/scala-3/tethys/derivation/ConfigurationMacroUtils.scala b/modules/core/src/main/scala-3/tethys/derivation/ConfigurationMacroUtils.scala
index b4193ba..519b8c7 100644
--- a/modules/core/src/main/scala-3/tethys/derivation/ConfigurationMacroUtils.scala
+++ b/modules/core/src/main/scala-3/tethys/derivation/ConfigurationMacroUtils.scala
@@ -689,7 +689,7 @@ trait ConfigurationMacroUtils:
             )
           )
 
-        val discriminators: List[Term] = getAllChildren(tpe).map {
+        val discriminators: List[Term] = getAllChildren(tpe).distinct.map {
           case tpe: TypeRef =>
             Select(stub(tpe), symbol)
           case tpe: TermRef =>
diff --git a/modules/core/src/main/scala-3/tethys/derivation/Derivation.scala b/modules/core/src/main/scala-3/tethys/derivation/Derivation.scala
index 688c9bc..234ae70 100644
--- a/modules/core/src/main/scala-3/tethys/derivation/Derivation.scala
+++ b/modules/core/src/main/scala-3/tethys/derivation/Derivation.scala
@@ -149,7 +149,7 @@ private[derivation] class DerivationMacro(val quotes: Quotes)
   ): Expr[JsonObjectWriter[T]] =
     val tpe = TypeRepr.of[T]
     val parsedConfig = parseSumConfig[T]
-    val types = getAllChildren(tpe)
+    val types = getAllChildren(tpe).distinct
     val (missingWriters, refs) = deriveMissingWritersForSum(types)
     val mirror = '{ summonInline[Mirror.SumOf[T]] }
     val writer = Block(
@@ -492,7 +492,7 @@ private[derivation] class DerivationMacro(val quotes: Quotes)
   def deriveJsonReaderForSum[T: Type]: Expr[JsonReader[T]] =
     val tpe = TypeRepr.of[T]
     val parsed = parseSumConfig[T]
-    val children = getAllChildren(tpe)
+    val children = getAllChildren(tpe).distinct
     parsed.discriminator match
       case Some(DiscriminatorConfig(label, tpe, discriminators)) =>
         tpe.asType match