diff --git a/.scalafmt.conf b/.scalafmt.conf
index da95c0a..f08905f 100644
--- a/.scalafmt.conf
+++ b/.scalafmt.conf
@@ -11,3 +11,12 @@ optIn.breakChainOnFirstMethodDot = false
 trailingCommas = preserve
 version = "3.7.17"
 project.layout = StandardConvention
+rewrite.scala3.convertToNewSyntax = true
+fileOverride {
+  "glob:**/src/**/scala-3/**" {
+    rewrite.scala3.convertToNewSyntax = false
+  }
+}
+runner.dialectOverride.allowSignificantIndentation = false
+runner.dialectOverride.allowAsForImportRename = false
+runner.dialectOverride.allowStarWildcardImport = false
diff --git a/core/jvm/src/test/scala/scalapb_argonaut/JavaAssertionsPlatform.scala b/core/jvm/src/test/scala/scalapb_argonaut/JavaAssertionsPlatform.scala
index c712800..4161e77 100644
--- a/core/jvm/src/test/scala/scalapb_argonaut/JavaAssertionsPlatform.scala
+++ b/core/jvm/src/test/scala/scalapb_argonaut/JavaAssertionsPlatform.scala
@@ -10,7 +10,7 @@ import JsonFormatSpecBase.assertThrows
 trait JavaAssertionsPlatform {
   self: TestSuite with JavaAssertions =>
 
-  def registeredCompanions: Seq[GeneratedMessageCompanion[_]]
+  def registeredCompanions: Seq[GeneratedMessageCompanion[?]]
 
   val JavaJsonTypeRegistry =
     this.registeredCompanions
diff --git a/core/shared/src/main/scala/scalapb_argonaut/JsonFormat.scala b/core/shared/src/main/scala/scalapb_argonaut/JsonFormat.scala
index eec1f59..28d9cef 100644
--- a/core/shared/src/main/scala/scalapb_argonaut/JsonFormat.scala
+++ b/core/shared/src/main/scala/scalapb_argonaut/JsonFormat.scala
@@ -20,7 +20,7 @@ import scala.util.control.NonFatal
 case class Formatter[T](writer: (Printer, T) => Json, parser: (Parser, Json) => T)
 
 case class FormatRegistry(
-  messageFormatters: Map[Class[_], Formatter[_]] = Map.empty,
+  messageFormatters: Map[Class[?], Formatter[?]] = Map.empty,
   enumFormatters: Map[EnumDescriptor, EnumFormatter[EnumValueDescriptor]] = Map.empty,
   registeredCompanions: Seq[GenericCompanion] = Seq.empty
 ) {
@@ -45,11 +45,11 @@ case class FormatRegistry(
     registerMessageFormatter((p: Printer, t: T) => writer(t), (p: Parser, v: Json) => parser(v))
   }
 
-  def getMessageWriter[T](klass: Class[_ <: T]): Option[(Printer, T) => Json] = {
+  def getMessageWriter[T](klass: Class[? <: T]): Option[(Printer, T) => Json] = {
     messageFormatters.get(klass).asInstanceOf[Option[Formatter[T]]].map(_.writer)
   }
 
-  def getMessageParser[T](klass: Class[_ <: T]): Option[(Parser, Json) => T] = {
+  def getMessageParser[T](klass: Class[? <: T]): Option[(Parser, Json) => T] = {
     messageFormatters.get(klass).asInstanceOf[Option[Formatter[T]]].map(_.parser)
   }
 
@@ -371,7 +371,7 @@ class Parser private (config: Parser.ParserConfig) {
   }
 
   private def fromJsonToPMessage(
-    cmp: GeneratedMessageCompanion[_],
+    cmp: GeneratedMessageCompanion[?],
     value: Json,
     skipTypeUrl: Boolean
   ): PMessage = {
@@ -502,7 +502,7 @@ class Parser private (config: Parser.ParserConfig) {
   }
 
   protected def parseSingleValue(
-    containerCompanion: GeneratedMessageCompanion[_],
+    containerCompanion: GeneratedMessageCompanion[?],
     fd: FieldDescriptor,
     value: Json
   ): PValue =
diff --git a/core/shared/src/test/scala/scalapb_argonaut/JavaAssertions.scala b/core/shared/src/test/scala/scalapb_argonaut/JavaAssertions.scala
index e5a0ce6..04f20d1 100644
--- a/core/shared/src/test/scala/scalapb_argonaut/JavaAssertions.scala
+++ b/core/shared/src/test/scala/scalapb_argonaut/JavaAssertions.scala
@@ -6,7 +6,7 @@ import scalapb_json._
 
 trait JavaAssertions extends JavaAssertionsPlatform { self: utest.TestSuite =>
 
-  def registeredCompanions: Seq[GeneratedMessageCompanion[_]] = Seq.empty
+  def registeredCompanions: Seq[GeneratedMessageCompanion[?]] = Seq.empty
 
   val ScalaTypeRegistry = registeredCompanions.foldLeft(TypeRegistry.empty)((r, c) =>
     r.addMessageByCompanion(c.asInstanceOf[GenericCompanion])