diff --git a/build.sbt b/build.sbt
index ea7ed229a5..25a13675ce 100644
--- a/build.sbt
+++ b/build.sbt
@@ -931,7 +931,7 @@ lazy val sprayJson = (projectMatrix in file("json/spray-json"))
     ),
     scalaTest
   )
-  .jvmPlatform(scalaVersions = scala2)
+  .jvmPlatform(scalaVersions = scala2 ++ scala3)
   .dependsOn(core, jsonCommon)
 
 lazy val play29Json = (projectMatrix in file("json/play29-json"))
@@ -971,7 +971,7 @@ lazy val prometheusBackend = (projectMatrix in file("observability/prometheus-ba
   .settings(
     name := "prometheus-backend",
     libraryDependencies ++= Seq(
-      "io.prometheus" % "prometheus-metrics-core" % "1.3.0"
+      "io.prometheus" % "prometheus-metrics-core" % "1.3.1"
     ),
     scalaTest
   )
diff --git a/json/spray-json/src/test/scala/sttp/client4/SprayJsonTests.scala b/json/spray-json/src/test/scala/sttp/client4/SprayJsonTests.scala
index 873c8186fa..88086c4c0d 100644
--- a/json/spray-json/src/test/scala/sttp/client4/SprayJsonTests.scala
+++ b/json/spray-json/src/test/scala/sttp/client4/SprayJsonTests.scala
@@ -2,11 +2,12 @@ package sttp.client4
 
 import org.scalatest.EitherValues
 import spray.json.DefaultJsonProtocol._
+import spray.json.DefaultJsonProtocol.RootJsObjectFormat
 import spray.json.JsonParser.ParsingException
 import spray.json.{DeserializationException => _, _}
 import sttp.client4.SprayJsonTests._
 import sttp.client4.internal.Utf8
-import sttp.client4.sprayJson._
+import sttp.client4.sprayJson.{sprayBodySerializer, _}
 import sttp.model._
 import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers
@@ -14,6 +15,8 @@ import org.scalatest.matchers.should.Matchers
 class SprayJsonTests extends AnyFlatSpec with Matchers with EitherValues {
   behavior of "The spray-json module"
 
+  implicit private val jsObjectSerializer: BodySerializer[JsObject] = sprayBodySerializer(RootJsObjectFormat)
+
   it should "encode arbitrary json bodies" in {
     val body = Outer(Inner(42, true, "horses"), "cats")