diff --git a/.jvmopts b/.jvmopts
new file mode 100644
index 0000000..7fecadb
--- /dev/null
+++ b/.jvmopts
@@ -0,0 +1 @@
+-Dfile.encoding=UTF-8
diff --git a/README.md b/README.md
index 73664e2..bb37c23 100644
--- a/README.md
+++ b/README.md
@@ -7,11 +7,11 @@ but perhaps shows off a few standard library APIs.
 ## Building
 
 1. Update the highlights notes in `hand-written.md`.
-2. run `sbt -Dfile.encoding=UTF-8`, and then:
+2. run `sbt`, and then:
 ```
 > runMain MakeReleaseNotes $PrevVersion $CurrentVersion $ReleaseYear/$ReleaseMonth/$ReleaseDay "$pathToScalaScalaCheckout"
 ```
 
 ## Contributing
 
-Feel free to improve.   Make sure to sign the Scala CLA.
+Feel free to improve. Make sure to sign the Scala CLA.
diff --git a/build.sbt b/build.sbt
index ab05af2..fc19391 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,14 +1,11 @@
 name := "make-release-notes"
 
 scalaVersion := "2.13.8"
-
-scalacOptions ++= Seq("-feature", "-deprecation", "-Xfatal-warnings")
-
-libraryDependencies += "org.pegdown" % "pegdown" % "1.6.0"
-libraryDependencies += "org.apache.commons" % "commons-text" % "1.9"
-libraryDependencies += "org.scala-lang.modules" %% "scala-xml" % "2.0.1"
-
-{
-  require(sys.props("file.encoding") == "UTF-8", "Please rerun with -Dfile.encoding=UTF-8")
-  Nil
-}
+scalacOptions ++= Seq("-feature", "-deprecation", "-Werror")
+
+libraryDependencies ++= Seq(
+  "org.pegdown" % "pegdown" % "1.6.0",
+  "org.apache.commons" % "commons-text" % "1.9",
+  "org.scala-lang.modules" %% "scala-xml" % "2.0.1",
+  "org.scala-lang.modules" %% "scala-parallel-collections" % "1.0.3",
+)
diff --git a/project/plugins.sbt b/project/plugins.sbt
new file mode 100644
index 0000000..487b6eb
--- /dev/null
+++ b/project/plugins.sbt
@@ -0,0 +1,7 @@
+locally {
+  require(sys.props("file.encoding") == "UTF-8",
+    "Please rerun with -Dfile.encoding=UTF-8")
+  Nil
+}
+
+scalacOptions ++= Seq("-feature", "-deprecation", "-Xfatal-warnings")
diff --git a/src/main/scala/GitInfo.scala b/src/main/scala/GitInfo.scala
index bd35ce1..2551f9f 100644
--- a/src/main/scala/GitInfo.scala
+++ b/src/main/scala/GitInfo.scala
@@ -1,3 +1,4 @@
+import scala.collection.parallel.CollectionConverters._ // for .par
 
 case class Commit(sha: String, author: String, header: String, body: String) {
   def trimmedHeader = header.take(80)
@@ -9,11 +10,11 @@ object GitHelper {
   def processGitCommits(gitDir: java.io.File, previousTag: String, currentTag: String): IndexedSeq[Commit] = {
     import sys.process._
     val gitFormat = "%h %s" // sha and subject
-    val log = Process(Seq("git", "--no-pager", "log", s"${previousTag}..${currentTag}", "--format=format:" + gitFormat, "--no-merges", "--topo-order"), gitDir).lineStream
+    val log = Process(Seq("git", "--no-pager", "log", s"${previousTag}..${currentTag}", "--format=format:" + gitFormat, "--no-merges", "--topo-order"), gitDir).lazyLines
 
     log.par.map(_.split(" ", 2)).collect {
       case Array(sha, title) =>
-        val (author :: body) = Process(Seq("git", "--no-pager", "show", sha, "--format=format:%aN%n%b", "--quiet"), gitDir).lineStream.toList
+        val (author :: body) = Process(Seq("git", "--no-pager", "show", sha, "--format=format:%aN%n%b", "--quiet"), gitDir).lazyLines.toList
         Commit(sha, author, title, body.mkString("\n"))
     }.toVector
   }
@@ -41,10 +42,12 @@ class GitInfo(gitDir: java.io.File, val previousTag: String, val currentTag: Str
   import GitHelper._
   val commits = processGitCommits(gitDir, previousTag, currentTag)
 
-  val authors: Seq[(String, Int)] = {
-    val grouped: Vector[(String, Int)] = (commits groupBy (_.author)).map { case (a, c) => a -> c.length } { collection.breakOut }
-    (grouped sortBy (_._2)).reverse
-  }
+  val authors: Seq[(String, Int)] =
+    commits
+      .groupBy(_.author)
+      .map{case (a, c) => a -> c.length}
+      .toVector
+      .sortBy(_._2)
 
   val fixCommits =
     for {
diff --git a/src/main/scala/IO.scala b/src/main/scala/IO.scala
index 3f9064b..6fd889a 100644
--- a/src/main/scala/IO.scala
+++ b/src/main/scala/IO.scala
@@ -1,8 +1,8 @@
 import java.io.File
 
 object IO {
-  def write(f: java.io.File, contents: String) {
-  	val buf = new java.io.BufferedWriter(new java.io.FileWriter(f))
+  def write(f: java.io.File, contents: String): Unit = {
+    val buf = new java.io.BufferedWriter(new java.io.FileWriter(f))
     try buf.write(contents)
     finally buf.close()
   }
diff --git a/src/main/scala/MakeDownloadPage.scala b/src/main/scala/MakeDownloadPage.scala
index 043769c..fd03d94 100644
--- a/src/main/scala/MakeDownloadPage.scala
+++ b/src/main/scala/MakeDownloadPage.scala
@@ -18,7 +18,7 @@ class MakeDownloadPage(version: String, releaseDate: Date = new Date()) {
     import scala.sys.process._
     println("## fetching size of "+ url)
     scala.util.Try {
-      val responseHeader = Process(s"curl -m 5 --silent -D - -X HEAD $url").lineStream
+      val responseHeader = Process(s"curl -m 5 --silent -D - -X HEAD $url").lazyLines
       val contentLength = responseHeader.map(_.toLowerCase).find(_.startsWith("content-length"))
       val bytes = contentLength.map(_.split(":",2)(1).trim.toInt)
       bytes map (b => (responseHeader.head, b))
diff --git a/src/main/scala/MakeReleaseNotes.scala b/src/main/scala/MakeReleaseNotes.scala
index fc3fabc..6c4b337 100644
--- a/src/main/scala/MakeReleaseNotes.scala
+++ b/src/main/scala/MakeReleaseNotes.scala
@@ -37,9 +37,10 @@ object MakeReleaseNotes {
     }
   }
 
-  def apply(scalaDir: String, version: String, previousTag: String, currentTag: String, releaseDate: Date) {
-    Seq(Html, MarkDown).foreach(fmt => apply(new java.io.File(scalaDir), version, previousTag, currentTag, fmt, releaseDate))
-  }
+  def apply(scalaDir: String, version: String, previousTag: String, currentTag: String, releaseDate: Date): Unit =
+    Seq(Html, MarkDown).foreach(fmt =>
+      apply(new java.io.File(scalaDir), version, previousTag, currentTag, fmt, releaseDate))
+
   def apply(scalaDir: java.io.File, version: String, previousTag: String, currentTag: String, targetLanguage: TargetLanguage = MarkDown, releaseDate: Date = new Date()): Unit = {
     val out = targetLanguage match {
       case Html => new java.io.File("release-notes.html")
@@ -75,7 +76,7 @@ object MakeReleaseNotes {
     def rawHandWrittenNotes(file: java.io.File = new java.io.File(s"hand-written.md")): String = {
       val lines: List[String] = if (file.exists) {
         val src = Source.fromFile(file)
-        src.getLines.toList
+        src.getLines().toList
       } else Nil
       // if you don't have the next line, sub-bullets would be screwed!
       // please take this case into account and comment out 2 next lines and uncomment the line after!