diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index 4972c2aee..e88f2a811 100755
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -374,6 +374,7 @@ object Defaults extends BuildCommon {
     }
   )
 
+  // This is included into JvmPlugin.projectSettings
   def compileBase = inTask(console)(compilersSetting :: Nil) ++ compileBaseGlobal ++ Seq(
     incOptions := incOptions.value
       .withClassfileManagerType(
@@ -381,15 +382,8 @@ object Defaults extends BuildCommon {
           .of(crossTarget.value / "classes.bak", sbt.util.Logger.Null): ClassFileManagerType).toOptional
       ),
     scalaInstance := scalaInstanceTask.value,
-    crossVersion := (if (crossPaths.value) CrossVersion.binary else Disabled()),
-    scalaVersion := {
-      val scalaV = scalaVersion.value
-      val sv = (sbtBinaryVersion in pluginCrossBuild).value
-      val isPlugin = sbtPlugin.value
-      if (isPlugin) {
-        scalaVersionFromSbtBinaryVersion(sv)
-      } else scalaV
-    },
+    crossVersion := (if (crossPaths.value) CrossVersion.binary else CrossVersion.disabled),
+    scalaVersion := PluginCross.scalaVersionSetting.value,
     sbtBinaryVersion in pluginCrossBuild := binarySbtVersion(
       (sbtVersion in pluginCrossBuild).value),
     crossSbtVersions := Vector((sbtVersion in pluginCrossBuild).value),
@@ -426,14 +420,6 @@ object Defaults extends BuildCommon {
       derive(scalaBinaryVersion := binaryScalaVersion(scalaVersion.value))
     ))
 
-  private[sbt] def scalaVersionFromSbtBinaryVersion(sv: String): String =
-    VersionNumber(sv) match {
-      case VersionNumber(Seq(0, 12, _*), _, _) => "2.9.2"
-      case VersionNumber(Seq(0, 13, _*), _, _) => "2.10.6"
-      case VersionNumber(Seq(1, _, _*), _, _)  => "2.12.2"
-      case _                                   => sys.error(s"Unsupported sbt binary version: $sv")
-    }
-
   def makeCrossSources(scalaSrcDir: File,
                        javaSrcDir: File,
                        sv: String,
diff --git a/main/src/main/scala/sbt/PluginCross.scala b/main/src/main/scala/sbt/PluginCross.scala
index d39e1acac..8fb2d27ed 100644
--- a/main/src/main/scala/sbt/PluginCross.scala
+++ b/main/src/main/scala/sbt/PluginCross.scala
@@ -15,6 +15,9 @@ import Def.ScopedKey
 import sbt.internal.Load
 import sbt.internal.CommandStrings._
 import Cross.{ spacedFirst, requireSession }
+import sbt.librarymanagement.Configurations._
+import sbt.librarymanagement.VersionNumber
+import Project.inConfig
 
 /**
  * Module responsible for plugin cross building.
@@ -42,7 +45,10 @@ private[sbt] object PluginCross {
         val x = Project.extract(state)
         import x._
         state.log.info(s"Setting `sbtVersion in pluginCrossBuild` to $version")
-        val add = (sbtVersion in GlobalScope in pluginCrossBuild :== version) :: Nil
+        val add = List(sbtVersion in GlobalScope in pluginCrossBuild :== version) ++
+          inConfig(Compile)(List(scalaVersion := scalaVersionSetting.value)) ++
+          inConfig(Test)(List(scalaVersion := scalaVersionSetting.value))
+
         val cleared = session.mergeSettings.filterNot(crossExclude)
         val newStructure = Load.reapply(cleared ++ add, structure)
         Project.setProject(session, newStructure, command :: state)
@@ -74,4 +80,20 @@ private[sbt] object PluginCross {
         else versions.map(PluginSwitchCommand + " " + _ + " " + command) ::: current ::: state
     }
   }
+
+  def scalaVersionSetting: Def.Initialize[String] = Def.setting {
+    val scalaV = scalaVersion.value
+    val sv = (sbtBinaryVersion in pluginCrossBuild).value
+    val isPlugin = sbtPlugin.value
+    if (isPlugin) scalaVersionFromSbtBinaryVersion(sv)
+    else scalaV
+  }
+
+  def scalaVersionFromSbtBinaryVersion(sv: String): String =
+    VersionNumber(sv) match {
+      case VersionNumber(Seq(0, 12, _*), _, _) => "2.9.2"
+      case VersionNumber(Seq(0, 13, _*), _, _) => "2.10.6"
+      case VersionNumber(Seq(1, 0, _*), _, _)  => "2.12.2"
+      case _                                   => sys.error(s"Unsupported sbt binary version: $sv")
+    }
 }