diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index 360564cfb..34133efe1 100644
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -104,7 +104,6 @@ import sbt.SlashSyntax0._
 import sbt.internal.inc.{
   Analysis,
   AnalyzingCompiler,
-  Locate,
   ManagedLoggedReporter,
   MixedAnalyzingCompiler,
   ScalaInstance
@@ -759,13 +758,11 @@ object Defaults extends BuildCommon {
         Vector("-Ypickle-java", "-Ypickle-write", converter.toPath(earlyOutput.value).toString) ++ old
       else old
     },
+    persistJarClasspath :== true,
+    classpathDefinesClassCache := VirtualFileValueCache.definesClassCache(fileConverter.value),
     classpathEntryDefinesClassVF := {
-      val converter = fileConverter.value
-      val f = VirtualFileValueCache(converter)({ x: VirtualFile =>
-        if (x.name.toString != "rt.jar") Locate.definesClass(x)
-        else ((_: String) => false): DefinesClass
-      }).get
-      f
+      (if (persistJarClasspath.value) classpathDefinesClassCache.value
+       else VirtualFileValueCache.definesClassCache(fileConverter.value)).get
     },
     compileIncSetup := compileIncSetupTask.value,
     console := consoleTask.value,
diff --git a/main/src/main/scala/sbt/Keys.scala b/main/src/main/scala/sbt/Keys.scala
index 504b69a74..060fe0286 100644
--- a/main/src/main/scala/sbt/Keys.scala
+++ b/main/src/main/scala/sbt/Keys.scala
@@ -231,6 +231,8 @@ object Keys {
   val compilerCache = taskKey[GlobalsCache]("Cache of scala.tools.nsc.Global instances.  This should typically be cached so that it isn't recreated every task run.").withRank(DTask)
   val stateCompilerCache = AttributeKey[GlobalsCache]("stateCompilerCache", "Internal use: Global cache.")
   val classpathEntryDefinesClass = taskKey[File => DefinesClass]("Internal use: provides a function that determines whether the provided file contains a given class.").withRank(Invisible)
+  private[sbt] val classpathDefinesClassCache = settingKey[VirtualFileValueCache[DefinesClass]]("Internal use: a cache of jar classpath entries that persists across command evaluations.").withRank(Invisible)
+  val persistJarClasspath = settingKey[Boolean]("Toggles whether or not to cache jar classpath entries between command evaluations")
   val classpathEntryDefinesClassVF = taskKey[VirtualFile => DefinesClass]("Internal use: provides a function that determines whether the provided file contains a given class.").withRank(Invisible)
   val doc = taskKey[File]("Generates API documentation.").withRank(AMinusTask)
   val copyResources = taskKey[Seq[(File, File)]]("Copies resources to the output directory.").withRank(AMinusTask)
diff --git a/main/src/main/scala/sbt/internal/VirtualFileValueCache.scala b/main/src/main/scala/sbt/internal/VirtualFileValueCache.scala
index 56ca6ad78..02d107e83 100644
--- a/main/src/main/scala/sbt/internal/VirtualFileValueCache.scala
+++ b/main/src/main/scala/sbt/internal/VirtualFileValueCache.scala
@@ -11,7 +11,9 @@ package internal
 import java.util.concurrent.ConcurrentHashMap
 import sbt.internal.inc.Stamper
 import xsbti.{ FileConverter, VirtualFile, VirtualFileRef }
+import xsbti.compile.DefinesClass
 import xsbti.compile.analysis.{ Stamp => XStamp }
+import sbt.internal.inc.Locate
 
 /**
  * Cache based on path and its stamp.
@@ -22,6 +24,12 @@ sealed trait VirtualFileValueCache[A] {
 }
 
 object VirtualFileValueCache {
+  def definesClassCache(converter: FileConverter): VirtualFileValueCache[DefinesClass] = {
+    apply(converter) { x: VirtualFile =>
+      if (x.name.toString != "rt.jar") Locate.definesClass(x)
+      else (_: String) => false
+    }
+  }
   def apply[A](converter: FileConverter)(f: VirtualFile => A): VirtualFileValueCache[A] = {
     import collection.mutable.{ HashMap, Map }
     val stampCache: Map[VirtualFileRef, (Long, XStamp)] = new HashMap