diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/HttpHeaderParser.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/HttpHeaderParser.scala
index a6c3ac9a3d..2bbcb322fc 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/HttpHeaderParser.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/HttpHeaderParser.scala
@@ -493,7 +493,7 @@ private[http] object HttpHeaderParser {
     }
   }
 
-  @tailrec private def scanHeaderNameAndReturnIndexOfColon(input: ByteString, start: Int, limit: Int)(ix: Int = start): Int =
+  @tailrec private def scanHeaderNameAndReturnIndexOfColon(input: ByteString, start: Int, limit: Int)(ix: Int): Int =
     if (ix < limit)
       byteChar(input, ix) match {
         case ':'           ⇒ ix
diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/BodyPartRenderer.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/BodyPartRenderer.scala
index 9c94194bab..7f341060c4 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/BodyPartRenderer.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/BodyPartRenderer.scala
@@ -89,7 +89,7 @@ private[http] object BodyPartRenderer {
     r.get
   }
 
-  private def renderBoundary(r: Rendering, boundary: String, suppressInitialCrLf: Boolean = false): Unit = {
+  private def renderBoundary(r: Rendering, boundary: String, suppressInitialCrLf: Boolean): Unit = {
     if (!suppressInitialCrLf) r ~~ CrLf
     r ~~ '-' ~~ '-' ~~ boundary ~~ CrLf
   }
diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/ws/WebSocketClientBlueprint.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/ws/WebSocketClientBlueprint.scala
index 66274da944..2834c0c4c5 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/ws/WebSocketClientBlueprint.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/ws/WebSocketClientBlueprint.scala
@@ -101,7 +101,7 @@ object WebSocketClientBlueprint {
                   }
                 case Left(problem) ⇒
                   result.success(InvalidUpgradeResponse(response, s"WebSocket server at $uri returned $problem"))
-                  ctx.fail(throw new IllegalArgumentException(s"WebSocket upgrade did not finish because of '$problem'"))
+                  ctx.fail(new IllegalArgumentException(s"WebSocket upgrade did not finish because of '$problem'"))
               }
             case other ⇒
               throw new IllegalStateException(s"unexpected element of type ${other.getClass}")
diff --git a/akka-http-core/src/main/scala/akka/http/impl/model/parser/CommonRules.scala b/akka-http-core/src/main/scala/akka/http/impl/model/parser/CommonRules.scala
index e3df26bcde..7552cc130b 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/model/parser/CommonRules.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/model/parser/CommonRules.scala
@@ -420,7 +420,6 @@ private[parser] trait CommonRules { this: Parser with StringBuilding ⇒
       | oneOrMore(DIGIT) ~ push(999999999999999999L)) ~ OWS)
 
   private def digitInt(c: Char): Int = c - '0'
-  private def digitLong(c: Char): Long = (c - '0').toLong
 
   private def createDateTime(year: Int, month: Int, day: Int, hour: Int, min: Int, sec: Int, wkday: Int) = {
     val dt = DateTime(year, month, day, hour, min, sec)
diff --git a/akka-http-core/src/main/scala/akka/http/impl/model/parser/UriParser.scala b/akka-http-core/src/main/scala/akka/http/impl/model/parser/UriParser.scala
index 890da0906e..4d2d675b45 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/model/parser/UriParser.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/model/parser/UriParser.scala
@@ -228,7 +228,7 @@ private[http] class UriParser(val input: ParserInput,
   private def getDecodedString(charset: Charset = uriParsingCharset) =
     if (firstPercentIx >= 0) decode(sb.toString, charset, firstPercentIx)() else sb.toString
 
-  private def getDecodedStringAndLowerIfEncoded(charset: Charset = uriParsingCharset) =
+  private def getDecodedStringAndLowerIfEncoded(charset: Charset) =
     if (firstPercentIx >= 0) decode(sb.toString, charset, firstPercentIx)().toRootLowerCase else sb.toString
 
   private def createUriReference(): Uri = {
diff --git a/akka-http-core/src/main/scala/akka/http/impl/util/Rendering.scala b/akka-http-core/src/main/scala/akka/http/impl/util/Rendering.scala
index 1536221023..b606cdde24 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/util/Rendering.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/util/Rendering.scala
@@ -162,7 +162,7 @@ private[http] trait Rendering {
    */
   def ~~%(lng: Long): this.type =
     if (lng != 0) {
-      @tailrec def putChar(shift: Int = 60): this.type = {
+      @tailrec def putChar(shift: Int): this.type = {
         this ~~ CharUtils.lowerHexDigit(lng >>> shift)
         if (shift > 0) putChar(shift - 4) else this
       }
diff --git a/akka-http-core/src/main/scala/akka/http/impl/util/package.scala b/akka-http-core/src/main/scala/akka/http/impl/util/package.scala
index 34087ddccc..098928d1ac 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/util/package.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/util/package.scala
@@ -125,7 +125,7 @@ package util {
     override val shape = FlowShape(in, out)
 
     override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new TimerGraphStageLogic(shape) {
-      var bytes = ByteString.newBuilder
+      val bytes = ByteString.newBuilder
       private var emptyStream = false
 
       override def preStart(): Unit = scheduleOnce("ToStrictTimeoutTimer", timeout)