diff --git a/build.sc b/build.sc
index 0453944..21f45af 100644
--- a/build.sc
+++ b/build.sc
@@ -1,5 +1,7 @@
 import mill._, scalalib._, scalajslib._
 
+import scalajslib.api.ModuleKind
+
 import $file.fiftyforms.{build => ff}, ff.support._
 import $file.fiftyforms.{domain => dmn}, dmn.DomainModule
 
@@ -52,6 +54,8 @@
     domain.proof.command.client,
     endpoints.js
   )
+
+  def moduleKind = ModuleKind.ESModule
 }
 
 object server extends CommonModule with SbtModule {

diff --git a/build.sc b/build.sc
index 0453944..21f45af 100644
--- a/build.sc
+++ b/build.sc
@@ -1,5 +1,7 @@
 import mill._, scalalib._, scalajslib._
 
+import scalajslib.api.ModuleKind
+
 import $file.fiftyforms.{build => ff}, ff.support._
 import $file.fiftyforms.{domain => dmn}, dmn.DomainModule
 
@@ -52,6 +54,8 @@
     domain.proof.command.client,
     endpoints.js
   )
+
+  def moduleKind = ModuleKind.ESModule
 }
 
 object server extends CommonModule with SbtModule {
diff --git a/fiftyforms/build.sc b/fiftyforms/build.sc
index df64eb0..6d94c6a 100644
--- a/fiftyforms/build.sc
+++ b/fiftyforms/build.sc
@@ -47,16 +47,20 @@
       }
     }
 
+    trait JsModule extends PlatformModule with CommonJSModule {
+      def platform = "js"
+    }
+
+    trait JvmModule extends PlatformModule {
+      def platform = "jvm"
+    }
+
     def platformModule(platform: String): JavaModule
   }
 
   trait PureCrossModule extends CrossPlatformModule {
-    object js extends PlatformModule {
-      def platform = "js"
-    }
-    object jvm extends PlatformModule {
-      def platform = "jvm"
-    }
+    object js extends JsModule
+    object jvm extends JvmModule
 
     def platformModule(platform: String): JavaModule = platform match {
       case "js" => js
@@ -65,12 +69,8 @@
   }
 
   trait PureCrossSbtModule extends CrossPlatformModule {
-    object js extends PlatformModule with SbtModule {
-      def platform = "js"
-    }
-    object jvm extends PlatformModule with SbtModule {
-      def platform = "jvm"
-    }
+    object js extends JsModule with SbtModule
+    object jvm extends JvmModule with SbtModule
 
     def platformModule(platform: String): JavaModule = platform match {
       case "js" => js
@@ -79,7 +79,7 @@
   }
 
   trait FullCrossSbtModule extends CrossPlatformModule {
-    trait FullPlatformModule extends PlatformModule {
+    trait FullSources extends PlatformModule {
       def sources = T.sources(
         millSourcePath / platform / "src" / "main" / "scala",
         millSourcePath / "shared" / "src" / "main" / "scala"
@@ -91,10 +91,10 @@
       )
     }
 
-    object js extends FullPlatformModule {
+    object js extends JsModule with FullSources {
       def platform = "js"
     }
-    object jvm extends FullPlatformModule {
+    object jvm extends JvmModule with FullSources {
       def platform = "jvm"
     }