diff --git a/main/src/main/scala/sbt/internal/LibraryManagement.scala b/main/src/main/scala/sbt/internal/LibraryManagement.scala
index e6e0ecbfa..41ffbf3f3 100644
--- a/main/src/main/scala/sbt/internal/LibraryManagement.scala
+++ b/main/src/main/scala/sbt/internal/LibraryManagement.scala
@@ -203,8 +203,12 @@ private[sbt] object LibraryManagement {
       case Left(w) =>
         throw w.resolveException
     }
+    val key = (m: ModuleID) => (m.organization, m.name, m.revision)
+    val originalKeys = dependencies.map(key).toSet
+    val transitiveOnly = report.allModules.filterNot(m => originalKeys contains key(m))
+    val mergedDependencies = dependencies ++ transitiveOnly
     val newConfig = config
-      .withModule(module.withDependencies(report.allModules))
+      .withModule(module.withDependencies(mergedDependencies))
     lm.updateClassifiers(newConfig, uwconfig, Vector(), log)
   }
 
diff --git a/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/build.sbt b/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/build.sbt
new file mode 100644
index 000000000..5ea88cc5b
--- /dev/null
+++ b/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/build.sbt
@@ -0,0 +1,32 @@
+ivyConfiguration := Def.uncached {
+  throw new RuntimeException("updateSbtClassifiers should use updateSbtClassifiers / ivyConfiguration")
+}
+
+dependencyResolution := Def.uncached {
+  throw new RuntimeException("updateSbtClassifiers should use updateSbtClassifiers / dependencyResolution")
+}
+
+lazy val root = (project in file("."))
+  .settings(
+    scalaVersion := "2.11.12",
+    scalaOrganization := "doesnt.exist",
+    name := "myProjectName",
+
+    TaskKey[Unit]("checkPluginsInUpdateSbtClassifiers") := Def.uncached {
+      val updateReport = updateSbtClassifiers.value
+      val moduleReports = updateReport.configurations.find(_.configuration.name == "default").get.modules
+
+      // Calling "distinct" as there are different entries for sources and javadoc classifiers with same module
+      val moduleIds = moduleReports.map(_.module).distinct
+      val moduleIdsShort = moduleIds.map(m => s"${m.organization}:${m.name}")
+
+      // Verify that the target plugin sbt-buildinfo is included in the output
+      // The plugin may be cross-versioned as sbt-buildinfo_sbt2_3, etc.
+      val hasBuildinfoPlugin = moduleIdsShort.exists(id => id.startsWith("com.eed3si9n:sbt-buildinfo"))
+      assert(
+        hasBuildinfoPlugin,
+        s"Plugin com.eed3si9n:sbt-buildinfo was not found in updateSbtClassifiers output. Found modules: ${moduleIdsShort.sorted.mkString(", ")}"
+      )
+    }
+  )
+
diff --git a/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/project/build.sbt b/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/project/build.sbt
new file mode 100644
index 000000000..bebd4da68
--- /dev/null
+++ b/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/project/build.sbt
@@ -0,0 +1,2 @@
+ThisBuild / pluginCrossBuild / sbtVersion := "2.0.0"
+
diff --git a/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/project/plugins.sbt b/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/project/plugins.sbt
new file mode 100644
index 000000000..4ef1cf760
--- /dev/null
+++ b/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/project/plugins.sbt
@@ -0,0 +1,3 @@
+// Add a plugin to test that it's included in updateSbtClassifiers output
+addSbtPlugin("com.eed3si9n" % "sbt-buildinfo" % "0.13.1")
+
diff --git a/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/test b/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/test
new file mode 100644
index 000000000..19e2b66ee
--- /dev/null
+++ b/sbt-app/src/sbt-test/dependency-management/i8405-update-sbt-classifiers-plugins/test
@@ -0,0 +1,5 @@
+> updateSbtClassifiers
+
+# see assertion definition in build.sbt
+> checkPluginsInUpdateSbtClassifiers
+
diff --git a/sbt-app/src/sbt-test/dependency-management/update-sbt-classifiers/build.sbt b/sbt-app/src/sbt-test/dependency-management/update-sbt-classifiers/build.sbt
index 7c483b453..b69cd7cde 100644
--- a/sbt-app/src/sbt-test/dependency-management/update-sbt-classifiers/build.sbt
+++ b/sbt-app/src/sbt-test/dependency-management/update-sbt-classifiers/build.sbt
@@ -39,11 +39,13 @@ lazy val root = (project in file("."))
         "com.swoval:file-tree-views",
         "com.typesafe:config",
         "com.typesafe:ssl-config-core_3",
+        "junit:junit",
         "net.java.dev.jna:jna",
         "net.java.dev.jna:jna-platform",
         "net.openhft:zero-allocation-hashing",
         "org.checkerframework:checker-qual",
         "org.fusesource.jansi:jansi",
+        "org.hamcrest:hamcrest-core",
         "org.jline:jline-builtins",
         "org.jline:jline-native",
         "org.jline:jline-reader",