diff --git a/bsp/src/mill/bsp/Constants.scala b/bsp/src/mill/bsp/Constants.scala
index 9dd59b05f48f..735b27f3d61d 100644
--- a/bsp/src/mill/bsp/Constants.scala
+++ b/bsp/src/mill/bsp/Constants.scala
@@ -6,6 +6,6 @@ private[mill] object Constants {
   val bspProtocolVersion = BuildInfo.bsp4jVersion
   val bspWorkerImplClass = "mill.bsp.worker.BspWorkerImpl"
   val bspWorkerBuildInfoClass = "mill.bsp.worker.BuildInfo"
-  val languages: Seq[String] = Seq("java", "scala")
+  val languages: Seq[String] = Seq("java", "scala", "kotlin")
   val serverName = "mill-bsp"
 }
diff --git a/build.mill b/build.mill
index 25b4c03e51f9..db132da71696 100644
--- a/build.mill
+++ b/build.mill
@@ -428,7 +428,8 @@ trait MillBaseTestsModule extends TestModule {
       s"-DTEST_SCALATEST_VERSION=${Deps.TestDeps.scalaTest.dep.version}",
       s"-DTEST_TEST_INTERFACE_VERSION=${Deps.sbtTestInterface.dep.version}",
       s"-DTEST_ZIOTEST_VERSION=${Deps.TestDeps.zioTest.dep.version}",
-      s"-DTEST_ZINC_VERSION=${Deps.zinc.dep.version}"
+      s"-DTEST_ZINC_VERSION=${Deps.zinc.dep.version}",
+      s"-DMILL_TEST_KOTLIN_VERSION=${Deps.kotlinCompiler.dep.version}"
     )
   }
 
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-compile-classpaths.json b/integration/ide/bsp-server/resources/fixtures/build-targets-compile-classpaths.json
index f67288640f08..f39f59fa7eba 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-compile-classpaths.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-compile-classpaths.json
@@ -8,6 +8,16 @@
         "file:///workspace/hello-java/compile-resources"
       ]
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "classpath": [
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib/<kotlin-version>/kotlin-stdlib-<kotlin-version>.jar",
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/annotations/<annotations-version>/annotations-<annotations-version>.jar",
+        "file:///workspace/hello-kotlin/compile-resources"
+      ]
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-dependency-modules.json b/integration/ide/bsp-server/resources/fixtures/build-targets-dependency-modules.json
index 2820a7f6c4ac..5dbf41724f10 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-dependency-modules.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-dependency-modules.json
@@ -6,6 +6,17 @@
       },
       "modules": []
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "modules": [
+        {
+          "name": "org.jetbrains.kotlin:kotlin-stdlib",
+          "version": "<kotlin-version>"
+        }
+      ]
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-dependency-sources.json b/integration/ide/bsp-server/resources/fixtures/build-targets-dependency-sources.json
index 1a0bee2bbee4..3be9d342e20a 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-dependency-sources.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-dependency-sources.json
@@ -6,6 +6,15 @@
       },
       "sources": []
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "sources": [
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib/<kotlin-version>/kotlin-stdlib-<kotlin-version>-sources.jar",
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/annotations/<annotations-version>/annotations-<annotations-version>-sources.jar"
+      ]
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-javac-options.json b/integration/ide/bsp-server/resources/fixtures/build-targets-javac-options.json
index 043b0582ab6f..65e5269db0d2 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-javac-options.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-javac-options.json
@@ -10,6 +10,18 @@
       ],
       "classDirectory": "file:///workspace/out/hello-java/compile.dest/classes"
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "options": [],
+      "classpath": [
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib/<kotlin-version>/kotlin-stdlib-<kotlin-version>.jar",
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/annotations/<annotations-version>/annotations-<annotations-version>.jar",
+        "file:///workspace/hello-kotlin/compile-resources"
+      ],
+      "classDirectory": "file:///workspace/out/hello-kotlin/compile.dest/classes"
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-jvm-run-environments.json b/integration/ide/bsp-server/resources/fixtures/build-targets-jvm-run-environments.json
index 585df6807fc6..40d001f52ff5 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-jvm-run-environments.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-jvm-run-environments.json
@@ -14,6 +14,22 @@
       "environmentVariables": {},
       "mainClasses": []
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "classpath": [
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib/<kotlin-version>/kotlin-stdlib-<kotlin-version>.jar",
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/annotations/<annotations-version>/annotations-<annotations-version>.jar",
+        "file:///workspace/hello-kotlin/compile-resources",
+        "file:///workspace/hello-kotlin/resources",
+        "file:///workspace/out/hello-kotlin/compile.dest/classes"
+      ],
+      "jvmOptions": [],
+      "workingDirectory": "/workspace",
+      "environmentVariables": {},
+      "mainClasses": []
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-jvm-test-environments.json b/integration/ide/bsp-server/resources/fixtures/build-targets-jvm-test-environments.json
index 585df6807fc6..40d001f52ff5 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-jvm-test-environments.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-jvm-test-environments.json
@@ -14,6 +14,22 @@
       "environmentVariables": {},
       "mainClasses": []
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "classpath": [
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib/<kotlin-version>/kotlin-stdlib-<kotlin-version>.jar",
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/annotations/<annotations-version>/annotations-<annotations-version>.jar",
+        "file:///workspace/hello-kotlin/compile-resources",
+        "file:///workspace/hello-kotlin/resources",
+        "file:///workspace/out/hello-kotlin/compile.dest/classes"
+      ],
+      "jvmOptions": [],
+      "workingDirectory": "/workspace",
+      "environmentVariables": {},
+      "mainClasses": []
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-output-paths.json b/integration/ide/bsp-server/resources/fixtures/build-targets-output-paths.json
index 12bebf136cf4..167fc54a654e 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-output-paths.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-output-paths.json
@@ -6,6 +6,12 @@
       },
       "outputPaths": []
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "outputPaths": []
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-resources.json b/integration/ide/bsp-server/resources/fixtures/build-targets-resources.json
index fc0ab5736d10..7360d1c92ffb 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-resources.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-resources.json
@@ -6,6 +6,12 @@
       },
       "resources": []
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "resources": []
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-scalac-options.json b/integration/ide/bsp-server/resources/fixtures/build-targets-scalac-options.json
index 043b0582ab6f..65e5269db0d2 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-scalac-options.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-scalac-options.json
@@ -10,6 +10,18 @@
       ],
       "classDirectory": "file:///workspace/out/hello-java/compile.dest/classes"
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "options": [],
+      "classpath": [
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib/<kotlin-version>/kotlin-stdlib-<kotlin-version>.jar",
+        "file:///coursier-cache/https/repo1.maven.org/maven2/org/jetbrains/annotations/<annotations-version>/annotations-<annotations-version>.jar",
+        "file:///workspace/hello-kotlin/compile-resources"
+      ],
+      "classDirectory": "file:///workspace/out/hello-kotlin/compile.dest/classes"
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/build-targets-sources.json b/integration/ide/bsp-server/resources/fixtures/build-targets-sources.json
index bb3032f88af8..ef73b2656fc9 100644
--- a/integration/ide/bsp-server/resources/fixtures/build-targets-sources.json
+++ b/integration/ide/bsp-server/resources/fixtures/build-targets-sources.json
@@ -12,6 +12,18 @@
         }
       ]
     },
+    {
+      "target": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "sources": [
+        {
+          "uri": "file:///workspace/hello-kotlin/src",
+          "kind": 2,
+          "generated": false
+        }
+      ]
+    },
     {
       "target": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/fixtures/initialize-build-result.json b/integration/ide/bsp-server/resources/fixtures/initialize-build-result.json
index 207de64635de..3e7a009526d5 100644
--- a/integration/ide/bsp-server/resources/fixtures/initialize-build-result.json
+++ b/integration/ide/bsp-server/resources/fixtures/initialize-build-result.json
@@ -6,19 +6,22 @@
     "compileProvider": {
       "languageIds": [
         "java",
-        "scala"
+        "scala",
+        "kotlin"
       ]
     },
     "testProvider": {
       "languageIds": [
         "java",
-        "scala"
+        "scala",
+        "kotlin"
       ]
     },
     "runProvider": {
       "languageIds": [
         "java",
-        "scala"
+        "scala",
+        "kotlin"
       ]
     },
     "debugProvider": {
diff --git a/integration/ide/bsp-server/resources/fixtures/workspace-build-targets.json b/integration/ide/bsp-server/resources/fixtures/workspace-build-targets.json
index 41f482a77d32..f38dccc829a7 100644
--- a/integration/ide/bsp-server/resources/fixtures/workspace-build-targets.json
+++ b/integration/ide/bsp-server/resources/fixtures/workspace-build-targets.json
@@ -26,6 +26,48 @@
         "javaVersion": "<java-version>"
       }
     },
+    {
+      "id": {
+        "uri": "file:///workspace/hello-kotlin"
+      },
+      "displayName": "hello-kotlin",
+      "baseDirectory": "file:///workspace/hello-kotlin",
+      "tags": [
+        "library",
+        "application"
+      ],
+      "languageIds": [
+        "java",
+        "scala",
+        "kotlin"
+      ],
+      "dependencies": [],
+      "capabilities": {
+        "canCompile": true,
+        "canTest": false,
+        "canRun": true,
+        "canDebug": false
+      },
+      "dataKind": "scala",
+      "data": {
+        "scalaOrganization": "org.scala-lang",
+        "scalaVersion": "<scala-version>",
+        "scalaBinaryVersion": "2.13",
+        "platform": 1,
+        "jars": [
+          "file:///coursier-cache/https/repo1.maven.org/maven2/org/scala-lang/scala-compiler/<scala-version>/scala-compiler-<scala-version>.jar",
+          "file:///coursier-cache/https/repo1.maven.org/maven2/org/scala-lang/scala-reflect/<scala-version>/scala-reflect-<scala-version>.jar",
+          "file:///coursier-cache/https/repo1.maven.org/maven2/org/scala-lang/scala-library/<scala-version>/scala-library-<scala-version>.jar",
+          "file:///coursier-cache/https/repo1.maven.org/maven2/io/github/java-diff-utils/java-diff-utils/<java-diff-utils-version>/java-diff-utils-<java-diff-utils-version>.jar",
+          "file:///coursier-cache/https/repo1.maven.org/maven2/org/jline/jline/<jline-version>/jline-<jline-version>.jar",
+          "file:///coursier-cache/https/repo1.maven.org/maven2/net/java/dev/jna/jna/<jna-version>/jna-<jna-version>.jar"
+        ],
+        "jvmBuildTarget": {
+          "javaHome": "file:///java-home/",
+          "javaVersion": "<java-version>"
+        }
+      }
+    },
     {
       "id": {
         "uri": "file:///workspace/hello-scala"
diff --git a/integration/ide/bsp-server/resources/project/build.mill b/integration/ide/bsp-server/resources/project/build.mill
index 086b5caa7981..7e625ea7058d 100644
--- a/integration/ide/bsp-server/resources/project/build.mill
+++ b/integration/ide/bsp-server/resources/project/build.mill
@@ -1,10 +1,13 @@
 package build
 
 import mill._
-import mill.scalalib._
 
-object `hello-java` extends JavaModule
+object `hello-java` extends scalalib.JavaModule
 
-object `hello-scala` extends ScalaModule {
+object `hello-scala` extends scalalib.ScalaModule {
   def scalaVersion = Option(System.getenv("MILL_TEST_SCALA_2_13_VERSION")).getOrElse(???)
 }
+
+object `hello-kotlin` extends kotlinlib.KotlinModule {
+  def kotlinVersion = Option(System.getenv("MILL_TEST_KOTLIN_VERSION")).getOrElse(???)
+}
diff --git a/integration/ide/bsp-server/src/BspServerTests.scala b/integration/ide/bsp-server/src/BspServerTests.scala
index 8f6e9afb66d2..120c43768998 100644
--- a/integration/ide/bsp-server/src/BspServerTests.scala
+++ b/integration/ide/bsp-server/src/BspServerTests.scala
@@ -42,9 +42,31 @@ object BspServerTests extends UtestIntegrationTestSuite {
             }
         }
 
-        val replaceAll = replaceAllValues(workspacePath) ++ scalaTransitiveSubstitutions ++ Seq(
-          scalaVersion -> "<scala-version>"
-        )
+        val kotlinVersion = sys.props.getOrElse("MILL_TEST_KOTLIN_VERSION", ???)
+        val kotlinTransitiveSubstitutions = {
+          val scalaFetchRes = coursierapi.Fetch.create()
+            .addDependencies(coursierapi.Dependency.of(
+              "org.jetbrains.kotlin",
+              "kotlin-stdlib",
+              kotlinVersion
+            ))
+            .fetchResult()
+          scalaFetchRes.getDependencies.asScala
+            .filter(dep => dep.getModule.getOrganization != "org.jetbrains.kotlin")
+            .map { dep =>
+              def basePath(version: String) =
+                s"${dep.getModule.getOrganization.split('.').mkString("/")}/${dep.getModule.getName}/$version/${dep.getModule.getName}-$version"
+              basePath(dep.getVersion) -> basePath(s"<${dep.getModule.getName}-version>")
+            }
+        }
+
+        val replaceAll = replaceAllValues(workspacePath) ++
+          scalaTransitiveSubstitutions ++
+          kotlinTransitiveSubstitutions ++
+          Seq(
+            scalaVersion -> "<scala-version>",
+            kotlinVersion -> "<kotlin-version>"
+          )
 
         compareWithGsonFixture(
           initRes,
diff --git a/kotlinlib/src/mill/kotlinlib/KotlinModule.scala b/kotlinlib/src/mill/kotlinlib/KotlinModule.scala
index 937ea8363479..6a81e5557e42 100644
--- a/kotlinlib/src/mill/kotlinlib/KotlinModule.scala
+++ b/kotlinlib/src/mill/kotlinlib/KotlinModule.scala
@@ -5,11 +5,12 @@
 package mill
 package kotlinlib
 
-import mill.api.{Loose, PathRef, Result}
+import mill.api.{Loose, PathRef, Result, internal}
 import mill.define.{Command, ModuleRef, Task}
 import mill.kotlinlib.worker.api.KotlinWorker
 import mill.scalalib.api.{CompilationResult, ZincWorkerApi}
-import mill.scalalib.{JavaModule, Lib, ZincWorkerModule}
+import mill.scalalib.bsp.{BspBuildTarget, BspModule}
+import mill.scalalib.{JavaModule, Lib, ScalaModule, ZincWorkerModule}
 import mill.util.Jvm
 import mill.util.Util.millProjectModule
 import mill.{Agg, T}
@@ -326,6 +327,54 @@ trait KotlinModule extends JavaModule { outer =>
 
   private[kotlinlib] def internalReportOldProblems: Task[Boolean] = zincReportCachedProblems
 
+  @internal
+  override def bspBuildTarget: BspBuildTarget = super.bspBuildTarget.copy(
+    // Mark the module as a Scala one, so that intellij-scala handles it (and deals fine with Kotlin code)
+    languageIds =
+      Seq(BspModule.LanguageId.Java, BspModule.LanguageId.Scala, BspModule.LanguageId.Kotlin),
+    canCompile = true,
+    canRun = true
+  )
+
+  /**
+   * Classpath of the Scala Compiler, to be passed to IntelliJ
+   */
+  def kotlinIntellijScalaCompilerClasspath: T[Agg[PathRef]] =
+    this match {
+      case scalaMod: ScalaModule => Task { scalaMod.scalaCompilerClasspath() }
+      case _ =>
+        Task {
+          defaultResolver().resolveDeps(
+            mill.scalalib.Lib.scalaCompilerIvyDeps(
+              "org.scala-lang",
+              scala.util.Properties.versionNumberString
+            ) ++
+              mill.scalalib.Lib.scalaRuntimeIvyDeps(
+                "org.scala-lang",
+                scala.util.Properties.versionNumberString
+              )
+          )
+        }
+    }
+
+  @internal
+  override def bspBuildTargetData: Task[Option[(String, AnyRef)]] =
+    this match {
+      case scalaMod: ScalaModule =>
+        ScalaModule.bspBuildTargetData(scalaMod)
+      case _ =>
+        Task.Anon {
+          Some(
+            ScalaModule.bspBuildTargetData(
+              "org.scala-lang",
+              scala.util.Properties.versionNumberString,
+              kotlinIntellijScalaCompilerClasspath(),
+              jvmBuildTarget
+            )
+          )
+        }
+    }
+
   /**
    * A test sub-module linked to its parent module best suited for unit-tests.
    */
diff --git a/scalalib/src/mill/scalalib/ScalaModule.scala b/scalalib/src/mill/scalalib/ScalaModule.scala
index 16ce9abf6c5a..082522a0692d 100644
--- a/scalalib/src/mill/scalalib/ScalaModule.scala
+++ b/scalalib/src/mill/scalalib/ScalaModule.scala
@@ -2,6 +2,7 @@ package mill
 package scalalib
 
 import mill.api.{DummyInputStream, JarManifest, PathRef, Result, internal}
+import mill.scalalib.bsp.JvmBuildTarget
 import mill.main.BuildInfo
 import mill.util.{Jvm, Util}
 import mill.util.Jvm.createJar
@@ -580,19 +581,8 @@ trait ScalaModule extends JavaModule with TestModule.ScalaModuleBase { outer =>
   )
 
   @internal
-  override def bspBuildTargetData: Task[Option[(String, AnyRef)]] = Task.Anon {
-    Some((
-      "scala",
-      ScalaBuildTarget(
-        scalaOrganization = scalaOrganization(),
-        scalaVersion = scalaVersion(),
-        scalaBinaryVersion = ZincWorkerUtil.scalaBinaryVersion(scalaVersion()),
-        platform = ScalaPlatform.JVM,
-        jars = scalaCompilerClasspath().map(_.path.toNIO.toUri.toString).iterator.toSeq,
-        jvmBuildTarget = Some(jvmBuildTarget)
-      )
-    ))
-  }
+  override def bspBuildTargetData: Task[Option[(String, AnyRef)]] =
+    ScalaModule.bspBuildTargetData(this)
 
   override def semanticDbScalaVersion: T[String] = scalaVersion()
 
@@ -652,3 +642,34 @@ trait ScalaModule extends JavaModule with TestModule.ScalaModuleBase { outer =>
       )
   }
 }
+
+object ScalaModule {
+  private[mill] def bspBuildTargetData(scalaMod: ScalaModule): Task[Option[(String, AnyRef)]] =
+    Task.Anon {
+      Some(
+        bspBuildTargetData(
+          scalaMod.scalaOrganization(),
+          scalaMod.scalaVersion(),
+          scalaMod.scalaCompilerClasspath(),
+          scalaMod.jvmBuildTarget
+        )
+      )
+    }
+  private[mill] def bspBuildTargetData(
+      scalaOrganization: String,
+      scalaVersion: String,
+      scalaCompilerClasspath: Agg[PathRef],
+      jvmBuildTarget: JvmBuildTarget
+  ): (String, AnyRef) =
+    (
+      "scala",
+      ScalaBuildTarget(
+        scalaOrganization = scalaOrganization,
+        scalaVersion = scalaVersion,
+        scalaBinaryVersion = ZincWorkerUtil.scalaBinaryVersion(scalaVersion),
+        platform = ScalaPlatform.JVM,
+        jars = scalaCompilerClasspath.map(_.path.toNIO.toUri.toString).iterator.toSeq,
+        jvmBuildTarget = Some(jvmBuildTarget)
+      )
+    )
+}
diff --git a/scalalib/src/mill/scalalib/bsp/BspModule.scala b/scalalib/src/mill/scalalib/bsp/BspModule.scala
index 42c386379874..edd208ca5795 100644
--- a/scalalib/src/mill/scalalib/bsp/BspModule.scala
+++ b/scalalib/src/mill/scalalib/bsp/BspModule.scala
@@ -46,6 +46,7 @@ object BspModule {
   object LanguageId {
     val Java = "java"
     val Scala = "scala"
+    val Kotlin = "kotlin"
   }
 
   /** Used to define the [[BspBuildTarget.tags]] field. */
diff --git a/testkit/src/mill/testkit/BspServerUtil.scala b/testkit/src/mill/testkit/BspServerUtil.scala
index eb15e27690ab..567e89e54f32 100644
--- a/testkit/src/mill/testkit/BspServerUtil.scala
+++ b/testkit/src/mill/testkit/BspServerUtil.scala
@@ -147,7 +147,7 @@ object BspServerUtil {
           BuildInfo.millVersion,
           b.Bsp4j.PROTOCOL_VERSION,
           workspacePath.toNIO.toUri.toASCIIString,
-          new b.BuildClientCapabilities(List("java", "scala").asJava)
+          new b.BuildClientCapabilities(List("java", "scala", "kotlin").asJava)
         )
       ).get()
 
diff --git a/testkit/src/mill/testkit/IntegrationTester.scala b/testkit/src/mill/testkit/IntegrationTester.scala
index d0ef5963e821..768cebe54cae 100644
--- a/testkit/src/mill/testkit/IntegrationTester.scala
+++ b/testkit/src/mill/testkit/IntegrationTester.scala
@@ -95,6 +95,9 @@ object IntegrationTester {
       Map("MILL_TEST_SUITE" -> this.getClass().toString()) ++
         sys.props.get("MILL_TEST_SCALA_2_13_VERSION")
           .map("MILL_TEST_SCALA_2_13_VERSION" -> _)
+          .toSeq ++
+        sys.props.get("MILL_TEST_KOTLIN_VERSION")
+          .map("MILL_TEST_KOTLIN_VERSION" -> _)
           .toSeq
 
     /**