diff --git a/main/settings/src/main/scala/sbt/Append.scala b/main/settings/src/main/scala/sbt/Append.scala
index 0d2f8062e..b558aab02 100644
--- a/main/settings/src/main/scala/sbt/Append.scala
+++ b/main/settings/src/main/scala/sbt/Append.scala
@@ -7,14 +7,14 @@ import sbt.internal.util.Attributed
 
 object Append {
   @implicitNotFound(msg = "No implicit for Append.Value[${A}, ${B}] found,\n  so ${B} cannot be appended to ${A}")
-  sealed trait Value[A, B] {
+  trait Value[A, B] {
     def appendValue(a: A, b: B): A
   }
   @implicitNotFound(msg = "No implicit for Append.Values[${A}, ${B}] found,\n  so ${B} cannot be appended to ${A}")
-  sealed trait Values[A, -B] {
+  trait Values[A, -B] {
     def appendValues(a: A, b: B): A
   }
-  sealed trait Sequence[A, -B, T] extends Value[A, T] with Values[A, B]
+  trait Sequence[A, -B, T] extends Value[A, T] with Values[A, B]
 
   implicit def appendSeq[T, V <: T]: Sequence[Seq[T], Seq[V], V] = new Sequence[Seq[T], Seq[V], V] {
     def appendValues(a: Seq[T], b: Seq[V]): Seq[T] = a ++ b
diff --git a/notes/0.13.10/drop-sealed-from-Append-typeclasses.markdown b/notes/0.13.10/drop-sealed-from-Append-typeclasses.markdown
new file mode 100644
index 000000000..6ad216120
--- /dev/null
+++ b/notes/0.13.10/drop-sealed-from-Append-typeclasses.markdown
@@ -0,0 +1,10 @@
+
+  [1171]: https://github.com/sbt/sbt/issues/1171
+  [2322]: https://github.com/sbt/sbt/pull/2322
+
+### Fixes with compatibility implications
+
+### Improvements
+- Drops `sealed` from the typeclasses in Append. [#2322][] by [@dwijnand][]
+
+### Bug fixes