diff --git a/build.sbt b/build.sbt
index 56ef792..4b6145e 100644
--- a/build.sbt
+++ b/build.sbt
@@ -72,7 +72,7 @@
 )
 
 // Compiler settings
-scalacOptions := Seq("-deprecation", "-language:postfixOps", "-opt:l:method")
+scalacOptions := Seq("-deprecation", "-language:postfixOps", "-opt:l:method", "-Xfuture")
 javacOptions in compile ++= Seq("-target", "8", "-source", "8")
 javaOptions in Jetty += "-Dlogback.configurationFile=/logback-dev.xml"
 
diff --git a/project/Checksums.scala b/project/Checksums.scala
index 7dfe120..65f87c6 100644
--- a/project/Checksums.scala
+++ b/project/Checksums.scala
@@ -18,7 +18,7 @@
       val buf = new Array[Byte](bufferSize)
       md.reset()
       @tailrec
-      def loop() {
+      def loop(): Unit = {
         val len = is read buf
         if (len != -1) {
           md update (buf, 0, len)
diff --git a/src/main/scala/ScalatraBootstrap.scala b/src/main/scala/ScalatraBootstrap.scala
index 5888f4e..70e4bf7 100644
--- a/src/main/scala/ScalatraBootstrap.scala
+++ b/src/main/scala/ScalatraBootstrap.scala
@@ -9,7 +9,7 @@
 import org.scalatra._
 
 class ScalatraBootstrap extends LifeCycle with SystemSettingsService {
-  override def init(context: ServletContext) {
+  override def init(context: ServletContext): Unit = {
 
     val settings = loadSystemSettings()
     if (settings.baseUrl.exists(_.startsWith("https://"))) {
diff --git a/src/main/scala/gitbucket/core/service/MergeService.scala b/src/main/scala/gitbucket/core/service/MergeService.scala
index 0ea90f7..0c907ce 100644
--- a/src/main/scala/gitbucket/core/service/MergeService.scala
+++ b/src/main/scala/gitbucket/core/service/MergeService.scala
@@ -71,7 +71,7 @@
     requestRepositoryName: String,
     requestBranch: String,
     issueId: Int
-  ) {
+  ): Unit = {
     using(Git.open(getRepositoryDir(userName, repositoryName))) { git =>
       git.fetch
         .setRemote(getRepositoryDir(requestUserName, requestRepositoryName).toURI.toString)
@@ -246,7 +246,7 @@
       val mergeTipCommit = using(new RevWalk(repository))(_.parseCommit(mergeTip))
       val committer = mergeTipCommit.getCommitterIdent
 
-      def _updateBranch(treeId: ObjectId, message: String, branchName: String) {
+      def _updateBranch(treeId: ObjectId, message: String, branchName: String): Unit = {
         // creates merge commit
         val mergeCommitId = createMergeCommit(treeId, committer, message)
         Util.updateRefs(repository, branchName, mergeCommitId, true, committer)
diff --git a/src/main/scala/gitbucket/core/ssh/GitCommand.scala b/src/main/scala/gitbucket/core/ssh/GitCommand.scala
index 0087915..8380e94 100644
--- a/src/main/scala/gitbucket/core/ssh/GitCommand.scala
+++ b/src/main/scala/gitbucket/core/ssh/GitCommand.scala
@@ -79,7 +79,7 @@
     this.in = in
   }
 
-  override def setSession(serverSession: ServerSession) {
+  override def setSession(serverSession: ServerSession): Unit = {
     this.authType = PublicKeyAuthenticator.getAuthType(serverSession)
   }
 
diff --git a/src/main/scala/gitbucket/core/util/SyntaxSugars.scala b/src/main/scala/gitbucket/core/util/SyntaxSugars.scala
index def4c3a..2ede323 100644
--- a/src/main/scala/gitbucket/core/util/SyntaxSugars.scala
+++ b/src/main/scala/gitbucket/core/util/SyntaxSugars.scala
@@ -11,7 +11,7 @@
 
   def defining[A, B](value: A)(f: A => B): B = f(value)
 
-  def using[A <% { def close(): Unit }, B](resource: A)(f: A => B): B =
+  def using[A <: { def close(): Unit }, B](resource: A)(f: A => B): B =
     try f(resource)
     finally {
       if (resource != null) {
@@ -21,7 +21,7 @@
       }
     }
 
-  def using[A <% { def close(): Unit }, B <% { def close(): Unit }, C](resource1: A, resource2: B)(f: (A, B) => C): C =
+  def using[A <: { def close(): Unit }, B <: { def close(): Unit }, C](resource1: A, resource2: B)(f: (A, B) => C): C =
     try f(resource1, resource2)
     finally {
       if (resource1 != null) {
diff --git a/src/test/scala/gitbucket/core/util/GitSpecUtil.scala b/src/test/scala/gitbucket/core/util/GitSpecUtil.scala
index 976778d..4bf8e0f 100644
--- a/src/test/scala/gitbucket/core/util/GitSpecUtil.scala
+++ b/src/test/scala/gitbucket/core/util/GitSpecUtil.scala
@@ -42,7 +42,7 @@
     autorName: String = "dummy",
     autorEmail: String = "dummy@example.com",
     message: String = "test commit"
-  ) {
+  ): Unit = {
     val builder = DirCache.newInCore.builder()
     val inserter = git.getRepository.newObjectInserter()
     val headId = git.getRepository.resolve(branch + "^{commit}")