diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index 18a4ac4d2..4f638203b 100644
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -4702,9 +4702,11 @@ object Classpaths:
     val app = appConfiguration.value
     def isJansiOrJLine(f: File) = f.getName.contains("jline") || f.getName.contains("jansi")
     val scalaInstanceJars = app.provider.scalaProvider.jars.filterNot(isJansiOrJLine)
+    // Sorted for the same reason as the metabuild classpath in `Load`.
     val sbtCp = (scalaInstanceJars ++ app.provider.mainClasspath)
       .map(_.toPath)
       .map(p => converter.toVirtualFile(p): HashedVirtualFileRef)
+      .sortBy(_.id)
       .map(Attributed.blank)
     val cpConfig = classpathConfiguration.value
     val up = update.value
diff --git a/main/src/main/scala/sbt/internal/Load.scala b/main/src/main/scala/sbt/internal/Load.scala
index 974aca615..d365b7557 100755
--- a/main/src/main/scala/sbt/internal/Load.scala
+++ b/main/src/main/scala/sbt/internal/Load.scala
@@ -100,8 +100,9 @@ private[sbt] object Load:
     val loader = getClass.getClassLoader
     val converter = MappedFileConverter(rootPaths, true)
     val cp0 = provider.mainClasspath.toIndexedSeq ++ scalaProvider.jars.toIndexedSeq
+    // The launcher's order is a directory listing, and this classpath is hashed into the compile key.
     val classpath = Attributed.blankSeq(
-      cp0.map(_.toPath).map(p => converter.toVirtualFile(p): HashedVirtualFileRef)
+      cp0.map(_.toPath).map(p => converter.toVirtualFile(p): HashedVirtualFileRef).sortBy(_.id)
     )
     val csrConfig = CoursierConfiguration()
       .withResolvers(Resolver.combineDefaultResolvers(Vector.empty).toVector)