diff --git a/main/Load.scala b/main/Load.scala
index 6f4fb83b3..73dc0bb38 100755
--- a/main/Load.scala
+++ b/main/Load.scala
@@ -4,7 +4,7 @@
 package sbt
 
 	import java.io.File
-	import java.net.URI
+	import java.net.{URI,URL}
 	import compiler.{Eval,EvalImports}
 	import xsbt.api.{Discovered,Discovery}
 	import classpath.ClasspathUtilities
@@ -519,13 +519,17 @@ object Load
 		new LoadedPlugins(dir, classpath, loader, plugins, pluginNames)
 	}
 	def getPluginNames(classpath: Seq[Attributed[File]], loader: ClassLoader): Seq[String] =
-		 ( binaryPlugins(loader) ++ (analyzed(classpath) flatMap findPlugins) ).distinct
+		 ( binaryPlugins(Build.data(classpath), loader) ++ (analyzed(classpath) flatMap findPlugins) ).distinct
 
-	def binaryPlugins(loader: ClassLoader): Seq[String] =
+	def binaryPlugins(classpath: Seq[File], loader: ClassLoader): Seq[String] =
 	{
 		import collection.JavaConversions._
-		loader.getResources("sbt/sbt.plugins").toSeq flatMap { u => IO.readLinesURL(u) map { _.trim } filter { !_.isEmpty } };
+		loader.getResources("sbt/sbt.plugins").toSeq.filter(onClasspath(classpath)) flatMap { u =>
+			IO.readLinesURL(u).map( _.trim).filter(!_.isEmpty)
+		}
 	}
+	def onClasspath(classpath: Seq[File])(url: URL): Boolean =
+		IO.urlAsFile(url) exists (classpath.contains _)
 
 	def loadPlugins(loader: ClassLoader, pluginNames: Seq[String]): Seq[Plugin] =
 		pluginNames.map(pluginName => loadPlugin(pluginName, loader))
diff --git a/sbt/src/sbt-test/project/source-plugins/build.sbt b/sbt/src/sbt-test/project/source-plugins/build.sbt
new file mode 100644
index 000000000..500e7835b
--- /dev/null
+++ b/sbt/src/sbt-test/project/source-plugins/build.sbt
@@ -0,0 +1,7 @@
+name := "source-plugins"
+
+organization := "org.example"
+
+ProguardPlugin.proguardSettings
+
+useJGit
\ No newline at end of file
diff --git a/sbt/src/sbt-test/project/source-plugins/project/project/Build.scala b/sbt/src/sbt-test/project/source-plugins/project/project/Build.scala
new file mode 100644
index 000000000..74665f0e1
--- /dev/null
+++ b/sbt/src/sbt-test/project/source-plugins/project/project/Build.scala
@@ -0,0 +1,7 @@
+import sbt._
+object PluginDef extends Build {
+  override def projects = Seq(root)
+  lazy val root = Project("plugins", file(".")) dependsOn(proguard, git)
+  lazy val proguard = uri("git://github.com/jsuereth/xsbt-proguard-plugin.git")
+  lazy val git = uri("git://github.com/sbt/sbt-git-plugin.git#scala-build")
+}
\ No newline at end of file
diff --git a/sbt/src/sbt-test/project/source-plugins/test b/sbt/src/sbt-test/project/source-plugins/test
new file mode 100644
index 000000000..08a542bb3
--- /dev/null
+++ b/sbt/src/sbt-test/project/source-plugins/test
@@ -0,0 +1,2 @@
+# just need to verify it loads
+> help
\ No newline at end of file
diff --git a/util/io/IO.scala b/util/io/IO.scala
index d3ff939af..d4afd1dc6 100644
--- a/util/io/IO.scala
+++ b/util/io/IO.scala
@@ -7,6 +7,7 @@ import Using._
 import ErrorHandling.translate
 
 import java.io.{BufferedReader, ByteArrayOutputStream, BufferedWriter, File, FileInputStream, InputStream, OutputStream, PrintWriter}
+import java.io.{ObjectInputStream, ObjectStreamClass}
 import java.net.{URI, URISyntaxException, URL}
 import java.nio.charset.Charset
 import java.util.Properties
@@ -65,18 +66,18 @@ object IO
 		catch { case _: URISyntaxException => new File(url.getPath) }
 
 	/** Converts the given URL to a File.  If the URL is for an entry in a jar, the File for the jar is returned. */
-	def asFile(url: URL): File =
-	{
+	def asFile(url: URL): File = urlAsFile(url) getOrElse error("URL is not a file: " + url)
+	def urlAsFile(url: URL): Option[File] =
 		url.getProtocol match
 		{
-			case "file" => toFile(url)
+			case "file" => Some(toFile(url))
 			case "jar" =>
 				val path = url.getPath
 				val end = path.indexOf('!')
-				new File(new URI(if(end == -1) path else path.substring(0, end)))
-			case _ => error("Invalid protocol " + url.getProtocol)
+				Some(new File(new URI(if(end == -1) path else path.substring(0, end))))
+			case _ => None
 		}
-	}
+
 	def assertDirectory(file: File) { assert(file.isDirectory, (if(file.exists) "Not a directory: " else "Directory not found: ") + file) }
 	def assertDirectories(file: File*) { file.foreach(assertDirectory) }
 
@@ -704,4 +705,13 @@ object IO
 	def assertAbsolute(uri: URI) = assert(uri.isAbsolute, "Not absolute: " + uri)
 
 	def parseClasspath(s: String): Seq[File] = IO.pathSplit(s).map(new File(_)).toSeq
+
+	def objectInputStream(wrapped: InputStream, loader: ClassLoader): ObjectInputStream = new ObjectInputStream(wrapped)
+	{
+		override def resolveClass(osc: ObjectStreamClass): Class[_] =
+		{
+			val c = Class.forName(osc.getName, false, loader)
+			if(c eq null) super.resolveClass(osc) else c
+		}
+	}
 }