diff --git a/docs/modules/ROOT/pages/large/multi-file-builds.adoc b/docs/modules/ROOT/pages/large/multi-file-builds.adoc
index d40b940ed24..4b94d0aee2d 100644
--- a/docs/modules/ROOT/pages/large/multi-file-builds.adoc
+++ b/docs/modules/ROOT/pages/large/multi-file-builds.adoc
@@ -9,8 +9,5 @@ include::partial$example/large/multi/10-multi-file-builds.adoc[]
 
 include::partial$example/large/multi/11-helper-files.adoc[]
 
-== Legacy `.sc` extension
-
-include::partial$example/large/multi/12-helper-files-sc.adoc[]
 
 
diff --git a/example/large/multi/11-helper-files/build.mill b/example/large/multi/11-helper-files/build.mill
index 1fde0fa661c..a2714f56d6e 100644
--- a/example/large/multi/11-helper-files/build.mill
+++ b/example/large/multi/11-helper-files/build.mill
@@ -5,8 +5,7 @@
 package build
 import $packages._
 import mill._, scalalib._
-import $file.foo.versions
-import $file.util.MyModule
+import foo.versions
 
 object `package` extends RootModule with MyModule {
   def forkEnv = Map(
diff --git a/example/large/multi/11-helper-files/foo/package.mill b/example/large/multi/11-helper-files/foo/package.mill
index a28fe0a29ce..d18830cde26 100644
--- a/example/large/multi/11-helper-files/foo/package.mill
+++ b/example/large/multi/11-helper-files/foo/package.mill
@@ -1,10 +1,9 @@
 package build.foo
 import mill._, scalalib._
-import $file.util
-import $file.foo.versions.myProjectVersion
-object `package` extends RootModule with build_.util.MyModule {
+import versions.myProjectVersion
+object `package` extends RootModule with build.MyModule {
   def forkEnv = Map(
-    "MY_SCALA_VERSION" -> util.myScalaVersion,
+    "MY_SCALA_VERSION" -> build.myScalaVersion,
     "MY_PROJECT_VERSION" -> myProjectVersion
   )
 }
diff --git a/example/large/multi/13-helper-files-mill-scala/build.mill.scala b/example/large/multi/12-helper-files-mill-scala/build.mill.scala
similarity index 91%
rename from example/large/multi/13-helper-files-mill-scala/build.mill.scala
rename to example/large/multi/12-helper-files-mill-scala/build.mill.scala
index 35ce38e6611..e5b74ab429f 100644
--- a/example/large/multi/13-helper-files-mill-scala/build.mill.scala
+++ b/example/large/multi/12-helper-files-mill-scala/build.mill.scala
@@ -1,13 +1,11 @@
 package build
 import $packages._
 import mill._, scalalib._
-import $file.foo.versions
-import $file.util.MyModule
 
 object `package` extends RootModule with MyModule {
   def forkEnv = Map(
     "MY_SCALA_VERSION" -> build.scalaVersion(),
-    "MY_PROJECT_VERSION" -> versions.myProjectVersion
+    "MY_PROJECT_VERSION" -> build.foo.myProjectVersion
   )
 }
 ///** See Also: util.mill.scala */
diff --git a/example/large/multi/12-helper-files-mill-scala/foo/package.mill.scala b/example/large/multi/12-helper-files-mill-scala/foo/package.mill.scala
new file mode 100644
index 00000000000..5dc502277a2
--- /dev/null
+++ b/example/large/multi/12-helper-files-mill-scala/foo/package.mill.scala
@@ -0,0 +1,8 @@
+package build.foo
+import mill._, scalalib._
+object `package` extends RootModule with build.MyModule {
+  def forkEnv = Map(
+    "MY_SCALA_VERSION" -> build.myScalaVersion,
+    "MY_PROJECT_VERSION" -> myProjectVersion
+  )
+}
diff --git a/example/large/multi/12-helper-files-sc/foo/src/Foo.scala b/example/large/multi/12-helper-files-mill-scala/foo/src/Foo.scala
similarity index 100%
rename from example/large/multi/12-helper-files-sc/foo/src/Foo.scala
rename to example/large/multi/12-helper-files-mill-scala/foo/src/Foo.scala
diff --git a/example/large/multi/13-helper-files-mill-scala/foo/versions.mill.scala b/example/large/multi/12-helper-files-mill-scala/foo/versions.mill.scala
similarity index 100%
rename from example/large/multi/13-helper-files-mill-scala/foo/versions.mill.scala
rename to example/large/multi/12-helper-files-mill-scala/foo/versions.mill.scala
diff --git a/example/large/multi/12-helper-files-sc/src/Main.scala b/example/large/multi/12-helper-files-mill-scala/src/Main.scala
similarity index 100%
rename from example/large/multi/12-helper-files-sc/src/Main.scala
rename to example/large/multi/12-helper-files-mill-scala/src/Main.scala
diff --git a/example/large/multi/13-helper-files-mill-scala/util.mill.scala b/example/large/multi/12-helper-files-mill-scala/util.mill.scala
similarity index 100%
rename from example/large/multi/13-helper-files-mill-scala/util.mill.scala
rename to example/large/multi/12-helper-files-mill-scala/util.mill.scala
diff --git a/example/large/multi/12-helper-files-sc/build.sc b/example/large/multi/12-helper-files-sc/build.sc
deleted file mode 100644
index e82973e3353..00000000000
--- a/example/large/multi/12-helper-files-sc/build.sc
+++ /dev/null
@@ -1,35 +0,0 @@
-// To ease the migration from Mill 0.11.x, the older `.sc` file extension is also supported
-// for Mill build files, and the `package` declaration is optional in such files. Note that
-// this means that IDE support using `.sc` files will not be as good as IDE support using the
-// current `.mill` extension with `package` declaration, so you should use `.mill` whenever
-// possible
-
-import mill._, scalalib._
-import $packages._
-import $file.foo.versions
-import $file.util, util.MyModule
-
-object `package` extends RootModule with MyModule {
-  def forkEnv = T {
-    Map(
-      "MY_SCALA_VERSION" -> build.scalaVersion(),
-      "MY_PROJECT_VERSION" -> versions.myProjectVersion
-    )
-  }
-}
-
-/** See Also: util.sc */
-/** See Also: foo/package.sc */
-/** See Also: foo/versions.sc */
-
-/** Usage
-
-> ./mill run
-Main Env build.util.myScalaVersion: 2.13.14
-Main Env build.foo.versions.myProjectVersion: 0.0.1
-
-> ./mill foo.run
-Foo Env build.util.myScalaVersion: 2.13.14
-Foo Env build.foo.versions.myProjectVersion: 0.0.1
-
-*/
diff --git a/example/large/multi/12-helper-files-sc/foo/package.sc b/example/large/multi/12-helper-files-sc/foo/package.sc
deleted file mode 100644
index 15c0e1ab727..00000000000
--- a/example/large/multi/12-helper-files-sc/foo/package.sc
+++ /dev/null
@@ -1,9 +0,0 @@
-import mill._, scalalib._
-import $file.^.util
-import $file.versions, versions.myProjectVersion
-object `package` extends RootModule with build_.util.MyModule {
-  def forkEnv = Map(
-    "MY_SCALA_VERSION" -> util.myScalaVersion,
-    "MY_PROJECT_VERSION" -> myProjectVersion
-  )
-}
diff --git a/example/large/multi/12-helper-files-sc/foo/versions.sc b/example/large/multi/12-helper-files-sc/foo/versions.sc
deleted file mode 100644
index 002f35f1335..00000000000
--- a/example/large/multi/12-helper-files-sc/foo/versions.sc
+++ /dev/null
@@ -1 +0,0 @@
-def myProjectVersion = "0.0.1"
diff --git a/example/large/multi/12-helper-files-sc/util.sc b/example/large/multi/12-helper-files-sc/util.sc
deleted file mode 100644
index dca710e79d8..00000000000
--- a/example/large/multi/12-helper-files-sc/util.sc
+++ /dev/null
@@ -1,7 +0,0 @@
-import mill._, scalalib._
-
-def myScalaVersion = "2.13.14"
-
-trait MyModule extends ScalaModule {
-  def scalaVersion = myScalaVersion
-}
diff --git a/example/large/multi/13-helper-files-mill-scala/foo/package.mill.scala b/example/large/multi/13-helper-files-mill-scala/foo/package.mill.scala
deleted file mode 100644
index a28fe0a29ce..00000000000
--- a/example/large/multi/13-helper-files-mill-scala/foo/package.mill.scala
+++ /dev/null
@@ -1,10 +0,0 @@
-package build.foo
-import mill._, scalalib._
-import $file.util
-import $file.foo.versions.myProjectVersion
-object `package` extends RootModule with build_.util.MyModule {
-  def forkEnv = Map(
-    "MY_SCALA_VERSION" -> util.myScalaVersion,
-    "MY_PROJECT_VERSION" -> myProjectVersion
-  )
-}
diff --git a/example/large/multi/13-helper-files-mill-scala/foo/src/Foo.scala b/example/large/multi/13-helper-files-mill-scala/foo/src/Foo.scala
deleted file mode 100644
index 08fe8028aac..00000000000
--- a/example/large/multi/13-helper-files-mill-scala/foo/src/Foo.scala
+++ /dev/null
@@ -1,8 +0,0 @@
-package foo
-
-object Foo {
-  def main(args: Array[String]): Unit = {
-    println("Foo Env build.util.myScalaVersion: " + sys.env("MY_SCALA_VERSION"))
-    println("Foo Env build.foo.versions.myProjectVersion: " + sys.env("MY_PROJECT_VERSION"))
-  }
-}
diff --git a/example/large/multi/13-helper-files-mill-scala/src/Main.scala b/example/large/multi/13-helper-files-mill-scala/src/Main.scala
deleted file mode 100644
index f8e6fdfa68f..00000000000
--- a/example/large/multi/13-helper-files-mill-scala/src/Main.scala
+++ /dev/null
@@ -1,6 +0,0 @@
-object Main {
-  def main(args: Array[String]): Unit = {
-    println("Main Env build.util.myScalaVersion: " + sys.env("MY_SCALA_VERSION"))
-    println("Main Env build.foo.versions.myProjectVersion: " + sys.env("MY_PROJECT_VERSION"))
-  }
-}
diff --git a/runner/src/mill/runner/CodeGen.scala b/runner/src/mill/runner/CodeGen.scala
index 6a588295615..05f9a37ed71 100644
--- a/runner/src/mill/runner/CodeGen.scala
+++ b/runner/src/mill/runner/CodeGen.scala
@@ -51,10 +51,10 @@ object CodeGen {
         }
         .distinct
 
-      val pkg = packageSegments.drop(1).dropRight(1)
+      val pkgSegments = packageSegments.drop(1).dropRight(1)
 
       def pkgSelector0(pre: Option[String], s: Option[String]) =
-        (pre ++ pkg ++ s).map(backtickWrap).mkString(".")
+        (pre ++ pkgSegments ++ s).map(backtickWrap).mkString(".")
       def pkgSelector2(s: Option[String]) = s"_root_.${pkgSelector0(Some(globalPackagePrefix), s)}"
       val (childSels, childAliases0) = childNames
         .map { c =>
@@ -67,7 +67,7 @@ object CodeGen {
         }.unzip
       val childAliases = childAliases0.mkString("\n")
 
-      val pkgLine = s"package ${pkgSelector0(Some(globalPackagePrefix), None)}"
+      val pkg = pkgSelector0(Some(globalPackagePrefix), None)
 
       val aliasImports = Seq(
         // `$file` as an alias for `build_` to make usage of `import $file` when importing
@@ -87,7 +87,7 @@ object CodeGen {
 
       val parts =
         if (!isBuildScript) {
-          s"""$pkgLine
+          s"""package $pkg
              |$aliasImports
              |object ${backtickWrap(scriptPath.last.split('.').head)} {
              |$markerComment
@@ -103,11 +103,16 @@ object CodeGen {
             scriptPath,
             scriptFolderPath,
             childAliases,
-            pkgLine,
+            pkg,
             aliasImports,
             scriptCode,
             markerComment,
-            parser
+            parser,
+            scriptSources
+              .map(_.path)
+              .filter(_ != scriptPath)
+              .filter(p => (p / os.up) == (scriptPath / os.up))
+              .map(_.last.split('.').head)
           )
         }
 
@@ -124,19 +129,25 @@ object CodeGen {
       scriptPath: os.Path,
       scriptFolderPath: os.Path,
       childAliases: String,
-      pkgLine: String,
+      pkg: String,
       aliasImports: String,
       scriptCode: String,
       markerComment: String,
-      parser: MillScalaParser
+      parser: MillScalaParser,
+      siblingScripts: Seq[String]
   ) = {
     val segments = scriptFolderPath.relativeTo(projectRoot).segments
 
-    val prelude = {
+    val exportSiblingScripts =
+      siblingScripts.map(s => s"export $pkg.${backtickWrap(s)}.*").mkString("\n")
+
+    val importSiblingScripts = siblingScripts
+      .map(s => s"import $pkg.${backtickWrap(s)}.*").mkString("\n")
+
+    val prelude =
       s"""import MillMiscInfo._
          |import _root_.mill.main.TokenReaders.given, _root_.mill.api.JsonFormatters.given
          |""".stripMargin
-    }
 
     val miscInfo =
       if (segments.nonEmpty) subfolderMiscInfo(scriptFolderPath, segments)
@@ -196,23 +207,32 @@ object CodeGen {
         newScriptCode = objectData.name.applyTo(newScriptCode, wrapperObjectName)
         newScriptCode = objectData.obj.applyTo(newScriptCode, "abstract class")
 
-        s"""$pkgLine
+        s"""package $pkg
            |$miscInfo
            |$aliasImports
+           |$importSiblingScripts
            |$prelude
            |$markerComment
            |$newScriptCode
            |object $wrapperObjectName extends $wrapperObjectName {
            |  ${childAliases.linesWithSeparators.mkString("  ")}
+           |  $exportSiblingScripts
            |  ${millDiscover(segments.nonEmpty)}
            |}""".stripMargin
 
       case None =>
-        s"""$pkgLine
+        s"""package $pkg
            |$miscInfo
            |$aliasImports
+           |$importSiblingScripts
            |$prelude
-           |${topBuildHeader(segments, scriptFolderPath, millTopLevelProjectRoot, childAliases)}
+           |${topBuildHeader(
+            segments,
+            scriptFolderPath,
+            millTopLevelProjectRoot,
+            childAliases,
+            exportSiblingScripts
+          )}
            |$markerComment
            |$scriptCode
            |}""".stripMargin
@@ -263,7 +283,8 @@ object CodeGen {
       segments: Seq[String],
       scriptFolderPath: os.Path,
       millTopLevelProjectRoot: os.Path,
-      childAliases: String
+      childAliases: String,
+      exportSiblingScripts: String
   ): String = {
     val extendsClause =
       if (segments.nonEmpty) s"extends _root_.mill.main.SubfolderModule "
@@ -277,8 +298,9 @@ object CodeGen {
     // path dependent types no longer match, e.g. for TokenReaders of custom types.
     // perhaps we can patch mainargs to substitute prefixes when summoning TokenReaders?
     // or, add an optional parameter to Discover.apply to substitute the outer class?
-    s"""object ${wrapperObjectName} extends $wrapperObjectName {
+    s"""object ${wrapperObjectName} extends $wrapperObjectName  {
        |  ${childAliases.linesWithSeparators.mkString("  ")}
+       |  $exportSiblingScripts
        |  ${millDiscover(segments.nonEmpty)}
        |}
        |abstract class $wrapperObjectName $extendsClause { this: $wrapperObjectName.type =>