diff --git a/sbt-test/source-dependencies/mirror-product/MyProduct.scala b/sbt-test/source-dependencies/mirror-product/MyProduct.scala
index acad1358f62b..ecc868c8d850 100644
--- a/sbt-test/source-dependencies/mirror-product/MyProduct.scala
+++ b/sbt-test/source-dependencies/mirror-product/MyProduct.scala
@@ -1 +1,3 @@
 case class MyProduct(x: Int)
+case class WillGetDefault(x: Int)
+case class WillChangeDefault(x: Int = 1)
diff --git a/sbt-test/source-dependencies/mirror-product/Test.scala b/sbt-test/source-dependencies/mirror-product/Test.scala
index e53d7b999517..826b0d181abc 100644
--- a/sbt-test/source-dependencies/mirror-product/Test.scala
+++ b/sbt-test/source-dependencies/mirror-product/Test.scala
@@ -8,3 +8,5 @@ transparent inline def foo[T](using m: Mirror.Of[T]): Int =
 
 @main def Test =
   assert(foo[MyProduct] == 2)
+  assert(summon[Mirror.Of[WillGetDefault]].defaultArgument(0) == 1)
+  assert(summon[Mirror.Of[WillChangeDefault]].defaultArgument(0) == 2)
diff --git a/sbt-test/source-dependencies/mirror-product/changes/MyProduct.scala b/sbt-test/source-dependencies/mirror-product/changes/MyProduct.scala
index 87e5af62bd7e..c98c40bd279c 100644
--- a/sbt-test/source-dependencies/mirror-product/changes/MyProduct.scala
+++ b/sbt-test/source-dependencies/mirror-product/changes/MyProduct.scala
@@ -1 +1,3 @@
 case class MyProduct(x: Int, y: String)
+case class WillGetDefault(x: Int = 1)
+case class WillChangeDefault(x: Int = 2)