diff --git a/build.sbt b/build.sbt
index 5571061a4..0af2d9bf9 100644
--- a/build.sbt
+++ b/build.sbt
@@ -845,7 +845,6 @@ lazy val `kamon-apache-cxf` = (project in file("instrumentation/kamon-apache-cxf
   .enablePlugins(JavaAgent)
   .settings(instrumentationSettings)
   .settings(
-    crossScalaVersions := Seq(`scala_2.13_version`, `scala_3_version`),
     libraryDependencies ++= Seq(
       kanelaAgent % "provided",
       "org.apache.cxf" % "cxf-rt-frontend-simple" % "3.3.6" % "provided",
diff --git a/instrumentation/kamon-apache-cxf/src/main/scala/kamon/instrumentation/apache/cxf/client/ApacheCxfClientHelper.scala b/instrumentation/kamon-apache-cxf/src/main/scala/kamon/instrumentation/apache/cxf/client/ApacheCxfClientHelper.scala
index 04cbeef17..eca265a1f 100644
--- a/instrumentation/kamon-apache-cxf/src/main/scala/kamon/instrumentation/apache/cxf/client/ApacheCxfClientHelper.scala
+++ b/instrumentation/kamon-apache-cxf/src/main/scala/kamon/instrumentation/apache/cxf/client/ApacheCxfClientHelper.scala
@@ -8,8 +8,7 @@ import org.slf4j.LoggerFactory
 import java.net.{URI, URISyntaxException}
 import java.util.Collections.{emptyMap => jEmptyMap, singletonList => jList}
 import java.util.{List => JList, Map => JMap}
-import scala.collection.mutable
-import scala.jdk.CollectionConverters.{ListHasAsScala, MapHasAsJava, MapHasAsScala}
+import scala.collection.JavaConverters._
 
 class ApacheCxfClientHelper
 
@@ -25,9 +24,10 @@ object ApacheCxfClientHelper {
       val uri: URI = getUri(request)
 
       override def write(header: String, value: String): Unit = {
-        val headers: mutable.Map[String, String] = getAllHeaders(delegate).to(mutable.Map)
-        headers.put(header, value)
-        delegate.put(Message.PROTOCOL_HEADERS, headers.map(m => m._1 -> jList(m._2)).toMap.asJava)
+        val builder = Map.newBuilder[String, JList[String]]
+        builder ++= getAllHeaders(delegate).map(m => m._1 -> jList(m._2))
+        builder += header -> jList(value)
+        delegate.put(Message.PROTOCOL_HEADERS, builder.result().asJava)
       }
 
       override def build(): Message = {
diff --git a/instrumentation/kamon-apache-cxf/src/test/scala/kamon/instrumentation/apache/cxf/client/util/MockServerExpectations.scala b/instrumentation/kamon-apache-cxf/src/test/scala/kamon/instrumentation/apache/cxf/client/util/MockServerExpectations.scala
index 252e15d06..42d1062c5 100644
--- a/instrumentation/kamon-apache-cxf/src/test/scala/kamon/instrumentation/apache/cxf/client/util/MockServerExpectations.scala
+++ b/instrumentation/kamon-apache-cxf/src/test/scala/kamon/instrumentation/apache/cxf/client/util/MockServerExpectations.scala
@@ -8,7 +8,7 @@ import org.mockserver.model.HttpRequest.request
 import org.mockserver.model.HttpResponse.response
 import org.slf4j.LoggerFactory
 
-import scala.jdk.CollectionConverters.SeqHasAsJava
+import scala.collection.JavaConverters._
 
 class MockServerExpectations(private val host: String, private val port: Int) {