diff --git a/build.sbt b/build.sbt
index 5b058c56..ff2bc24b 100644
--- a/build.sbt
+++ b/build.sbt
@@ -3,7 +3,7 @@ import ScalaModulePlugin._
 scalaVersionsByJvm in ThisBuild := {
   val v211 = "2.11.12"
   val v212 = "2.12.6"
-  val v213 = "2.13.0-M3"
+  val v213 = "2.13.0-M4"
 
   Map(
     6 -> List(v211 -> true),
@@ -38,7 +38,15 @@ lazy val `scala-parser-combinators` = crossProject.in(file(".")).
       "Scala Parser Combinators",
       "-doc-version",
       version.value
-    )
+    ),
+    unmanagedSourceDirectories in Compile ++= {
+      (unmanagedSourceDirectories in Compile).value.map { dir =>
+        CrossVersion.partialVersion(scalaVersion.value) match {
+          case Some((2, 13)) => file(dir.getPath ++ "-2.13")
+          case _             => file(dir.getPath ++ "-2.11-2.12")
+        }
+      }
+    }
   ).
   jvmSettings(
     OsgiKeys.exportPackage := Seq(s"scala.util.parsing.*;version=${version.value}"),
diff --git a/project/plugins.sbt b/project/plugins.sbt
index fdd0d207..66658960 100644
--- a/project/plugins.sbt
+++ b/project/plugins.sbt
@@ -1,3 +1,3 @@
 addSbtPlugin("org.scala-lang.modules" % "sbt-scala-module" % "1.0.14")
 
-addSbtPlugin("org.scala-js" % "sbt-scalajs" % "0.6.22")
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % "0.6.23")
diff --git a/shared/src/main/scala-2.11-2.12/scala/util/parsing/input/ScalaVersionSpecificPagedSeq.scala b/shared/src/main/scala-2.11-2.12/scala/util/parsing/input/ScalaVersionSpecificPagedSeq.scala
new file mode 100644
index 00000000..8ddd6bf5
--- /dev/null
+++ b/shared/src/main/scala-2.11-2.12/scala/util/parsing/input/ScalaVersionSpecificPagedSeq.scala
@@ -0,0 +1,5 @@
+package scala.util.parsing.input
+
+private[input] trait ScalaVersionSpecificPagedSeq[T] {
+  // Nothing for 2.11 and 2.12!
+}
\ No newline at end of file
diff --git a/shared/src/main/scala-2.13/scala/util/parsing/input/ScalaVersionSpecificPagedSeq.scala b/shared/src/main/scala-2.13/scala/util/parsing/input/ScalaVersionSpecificPagedSeq.scala
new file mode 100644
index 00000000..0c1ca5a9
--- /dev/null
+++ b/shared/src/main/scala-2.13/scala/util/parsing/input/ScalaVersionSpecificPagedSeq.scala
@@ -0,0 +1,7 @@
+package scala.util.parsing.input
+
+private[input] trait ScalaVersionSpecificPagedSeq[T] { self: PagedSeq[T] =>
+  // Members declared in scala.collection.Seq
+  override def iterableFactory: collection.SeqFactory[collection.IndexedSeq] = collection.IndexedSeq
+
+}
diff --git a/shared/src/main/scala/scala/util/parsing/input/PagedSeq.scala b/shared/src/main/scala/scala/util/parsing/input/PagedSeq.scala
index ba12ec28..1e775817 100644
--- a/shared/src/main/scala/scala/util/parsing/input/PagedSeq.scala
+++ b/shared/src/main/scala/scala/util/parsing/input/PagedSeq.scala
@@ -129,6 +129,7 @@ class PagedSeq[T: ClassTag] protected(
   end: Int)
 extends scala.collection.AbstractSeq[T]
    with scala.collection.IndexedSeq[T]
+   with ScalaVersionSpecificPagedSeq[T]
 {
   def this(more: (Array[T], Int, Int) => Int) = this(more, new Page[T](0), 0, UndeterminedEnd)
 
diff --git a/shared/src/test/scala/scala/util/parsing/combinator/UnitTestIO.scala b/shared/src/test/scala/scala/util/parsing/combinator/UnitTestIO.scala
index f754c682..10387eb4 100644
--- a/shared/src/test/scala/scala/util/parsing/combinator/UnitTestIO.scala
+++ b/shared/src/test/scala/scala/util/parsing/combinator/UnitTestIO.scala
@@ -25,7 +25,7 @@ class UnitTestIO {
     val s = "Here is a test string"
     val f = io.Source.fromBytes(s.getBytes("utf-8"))
     val b = new collection.mutable.ArrayBuffer[Char]()
-    f.copyToBuffer(b)
+    b ++= f
     assertEquals(new String(b.toArray), s)
   }
 }