diff --git a/DEVELOPING.md b/DEVELOPING.md
index 8b1db7b09..40cbfda3a 100644
--- a/DEVELOPING.md
+++ b/DEVELOPING.md
@@ -151,14 +151,14 @@ suite with `sbt testOnly`
 
 #### Integration tests
 
-Scripted integration tests reside in `sbt/src/sbt-test` and are
+Scripted integration tests reside in `sbt-app/src/sbt-test` and are
 written using the same testing infrastructure sbt plugin authors can
 use to test their own plugins with sbt. You can read more about this
 style of tests [here](https://www.scala-sbt.org/1.0/docs/Testing-sbt-plugins).
 
 You can run the integration tests with the `sbt scripted` sbt
 command. To run a single test, such as the test in
-`sbt/src/sbt-test/project/global-plugin`, simply run:
+`sbt-app/src/sbt-test/project/global-plugin`, simply run:
 
     sbt "scripted project/global-plugin"
 
diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index efd856a67..c199329f4 100644
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -1393,11 +1393,10 @@ object Defaults extends BuildCommon {
               val x = {
                 import analysis.{ apis, relations => rel }
                 rel.internalClassDeps(c).map(intlStamp(_, analysis, s + c)) ++
-                  rel.externalDeps(c).map(stamp) +
-                  (apis.internal.get(c) match {
-                    case Some(x) => x.compilationTimestamp
-                    case _       => Long.MinValue
-                  })
+                  rel.externalDeps(c).map(stamp) ++
+                  rel.productClassName.reverse(c).flatMap { pc =>
+                    apis.internal.get(pc).map(_.compilationTimestamp)
+                  } + Long.MinValue
               }.max
               if (x != Long.MinValue) {
                 stamps(c) = x
diff --git a/sbt-app/src/sbt-test/tests/test-quick/build.sbt b/sbt-app/src/sbt-test/tests/test-quick/build.sbt
index 0fb62b441..9fd396d27 100644
--- a/sbt-app/src/sbt-test/tests/test-quick/build.sbt
+++ b/sbt-app/src/sbt-test/tests/test-quick/build.sbt
@@ -1,9 +1,8 @@
 val scalatest = "org.scalatest" %% "scalatest" % "3.0.5"
-val scalaxml = "org.scala-lang.modules" %% "scala-xml" % "1.1.1"
 ThisBuild / scalaVersion := "2.12.12"
 
 lazy val root = (project in file("."))
   .settings(
-    libraryDependencies ++= List(scalaxml, scalatest),
+    libraryDependencies += scalatest % Test,
     Test / parallelExecution := false
   )
diff --git a/sbt-app/src/sbt-test/tests/test-quick/changed/MathFunction.scala b/sbt-app/src/sbt-test/tests/test-quick/changed/MathFunction.scala
new file mode 100644
index 000000000..1be75e613
--- /dev/null
+++ b/sbt-app/src/sbt-test/tests/test-quick/changed/MathFunction.scala
@@ -0,0 +1,3 @@
+object MathFunction {
+  def times2(i: Int): Int = 2 * 2
+}
diff --git a/sbt-app/src/sbt-test/tests/test-quick/src/main/scala/MathFunction.scala b/sbt-app/src/sbt-test/tests/test-quick/src/main/scala/MathFunction.scala
new file mode 100644
index 000000000..08d0ec501
--- /dev/null
+++ b/sbt-app/src/sbt-test/tests/test-quick/src/main/scala/MathFunction.scala
@@ -0,0 +1,3 @@
+object MathFunction {
+  def times2(i: Int): Int = i * 2
+}
diff --git a/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/Create.scala b/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/Create.scala
index 121de95b0..651807d8d 100644
--- a/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/Create.scala
+++ b/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/Create.scala
@@ -1,11 +1,10 @@
 import org.scalatest.FlatSpec
-import org.scalatest.matchers.ShouldMatchers
 
-class Create extends FlatSpec with ShouldMatchers with Base {
+class Create extends FlatSpec with Base {
   "a file" should "not exist" in {
 		A(new B).foo
-		marker.exists should equal(false)
-		marker.createNewFile() should equal (true)
+		assert(marker.exists == false)
+		assert(marker.createNewFile() == true)
   }
 
 }
diff --git a/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/Delete.scala b/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/Delete.scala
index cd2eb6617..ff1caacb1 100644
--- a/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/Delete.scala
+++ b/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/Delete.scala
@@ -1,9 +1,8 @@
 import org.scalatest.FlatSpec
-import org.scalatest.matchers.ShouldMatchers
 
-class Delete extends FlatSpec with ShouldMatchers with Base {
+class Delete extends FlatSpec with Base {
   "a file" should "exist" in {
-		marker.exists should equal(true)
+		assert(marker.exists == true)
 		marker.delete()
   }
 
diff --git a/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/MathFunctionSpec.scala b/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/MathFunctionSpec.scala
new file mode 100644
index 000000000..7ee6336da
--- /dev/null
+++ b/sbt-app/src/sbt-test/tests/test-quick/src/test/scala/MathFunctionSpec.scala
@@ -0,0 +1,7 @@
+import org.scalatest.FlatSpec
+
+class MathFunctionTest extends FlatSpec {
+  "times2" should "double the input" in {
+    assert(MathFunction.times2(4) == 8)
+  }
+}
diff --git a/sbt-app/src/sbt-test/tests/test-quick/disabled b/sbt-app/src/sbt-test/tests/test-quick/test
similarity index 82%
rename from sbt-app/src/sbt-test/tests/test-quick/disabled
rename to sbt-app/src/sbt-test/tests/test-quick/test
index d88f8a185..c86f0276f 100644
--- a/sbt-app/src/sbt-test/tests/test-quick/disabled
+++ b/sbt-app/src/sbt-test/tests/test-quick/test
@@ -32,3 +32,9 @@ $ sleep 2000
 -> testQuick Create
 > testQuick Delete
 > testQuick Create
+
+# https://github.com/sbt/sbt/issues/5504
+$ copy-file changed/MathFunction.scala src/test/scala/MathFunction.scala
+> compile
+$ sleep 2000
+-> testQuick MathFunctionTest