diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 234e7aa..3aa828f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -9,7 +9,7 @@ jobs:
       - uses: actions/checkout@v6
       - uses: coursier/setup-action@v3
         with:
-          jvm: temurin:8
+          jvm: temurin:21
           apps: sbt
       - uses: coursier/cache-action@v8
       - name: Run tests
diff --git a/build.sbt b/build.sbt
index fc99c6a..4ef16f0 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,5 +1,5 @@
 ThisBuild / organization := "io.latis-data"
-ThisBuild / scalaVersion := "3.3.9"
+ThisBuild / scalaVersion := "3.9.0"
 
 val fs2DataVersion = "1.8.1"
 val http4sVersion = "0.23.38"
diff --git a/src/main/scala/latis/service/hapi/DataService.scala b/src/main/scala/latis/service/hapi/DataService.scala
index c62ed22..e5c52b0 100644
--- a/src/main/scala/latis/service/hapi/DataService.scala
+++ b/src/main/scala/latis/service/hapi/DataService.scala
@@ -14,13 +14,13 @@ import org.log4s.*
 
 /** Implements the `/data` endpoint. */
 class DataService[F[_]: Concurrent](
-  alg: DataAlgebra[F] with InfoAlgebra[F]
+  alg: DataAlgebra[F] & InfoAlgebra[F]
 ) extends Http4sDsl[F] {
   import Format.*
   import Include.*
   import QueryDecoders.*
 
-  private[this] val logger = getLogger
+  private val logger = getLogger
 
   private def req2Resp(req: DataRequest, _params:Option[NonEmptyList[String]]): EitherT[F, Status, Response[F]] = {
     val dataset = req.dataset
diff --git a/src/main/scala/latis/service/hapi/InfoService.scala b/src/main/scala/latis/service/hapi/InfoService.scala
index 82ecb9c..28e991a 100644
--- a/src/main/scala/latis/service/hapi/InfoService.scala
+++ b/src/main/scala/latis/service/hapi/InfoService.scala
@@ -13,7 +13,7 @@ import org.log4s.*
 class InfoService[F[_]: Concurrent](alg: InfoAlgebra[F]) extends Http4sDsl[F] {
   import QueryDecoders.*
 
-  private[this] val logger = getLogger
+  private val logger = getLogger
 
   val service: HttpRoutes[F] =
     HttpRoutes.of[F] {
diff --git a/src/main/scala/latis/service/hapi/Latis3Interpreter.scala b/src/main/scala/latis/service/hapi/Latis3Interpreter.scala
index c0efbb5..77e9e6f 100644
--- a/src/main/scala/latis/service/hapi/Latis3Interpreter.scala
+++ b/src/main/scala/latis/service/hapi/Latis3Interpreter.scala
@@ -108,7 +108,7 @@ class Latis3Interpreter(catalog: Catalog) extends HapiInterpreter[IO] {
   override def streamJson(data: T, header: JsonObject): Stream[IO, Byte] = {
     val dataJson = new JsonEncoder().encode(data)
     val headerList = header.add("format", Json.fromString("json")).toList
-    val map = ListMap(headerList: _*)
+    val map = ListMap(headerList*)
     dataJson
       .through(json.ast.tokenize)
       .through(json.wrap.asArrayInObject(at = "data", in = map))