diff --git a/sbt/src/sbt-test/project/sequential/build.sbt b/sbt/src/sbt-test/project/sequential/build.sbt
index f3b423d13..cd4cb1eac 100644
--- a/sbt/src/sbt-test/project/sequential/build.sbt
+++ b/sbt/src/sbt-test/project/sequential/build.sbt
@@ -29,6 +29,8 @@ lazy val root = project.
       IO.append(t, "1")
     },
     sideEffect2 := {
+      // check for deduplication of tasks
+      val _ = sideEffect1.value
       val t = testFile.value
       IO.append(t, "2")
     },