diff --git a/akka-actor/src/main/scala/akka/actor/ActorSystem.scala b/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
index da31b9a28e..af28581891 100644
--- a/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
+++ b/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
@@ -21,6 +21,7 @@ import scala.concurrent.duration.{ FiniteDuration, Duration }
 import scala.concurrent.{ Await, Future, Promise, ExecutionContext, ExecutionContextExecutor }
 import scala.util.{ Failure, Success, Try }
 import scala.util.control.{ NonFatal, ControlThrowable }
+import java.util.Locale
 
 object ActorSystem {
 
@@ -181,7 +182,7 @@ object ActorSystem {
     final val LoggingFilter: String = getString("akka.logging-filter")
     final val LoggerStartTimeout: Timeout = Timeout(config.getMillisDuration("akka.logger-startup-timeout"))
     final val LogConfigOnStart: Boolean = config.getBoolean("akka.log-config-on-start")
-    final val LogDeadLetters: Int = config.getString("akka.log-dead-letters").toLowerCase match {
+    final val LogDeadLetters: Int = config.getString("akka.log-dead-letters").toLowerCase(Locale.ROOT) match {
       case "off" | "false" ⇒ 0
       case "on" | "true"   ⇒ Int.MaxValue
       case _               ⇒ config.getInt("akka.log-dead-letters")
diff --git a/akka-actor/src/main/scala/akka/event/Logging.scala b/akka-actor/src/main/scala/akka/event/Logging.scala
index 90b0f15278..4a6228c27d 100644
--- a/akka-actor/src/main/scala/akka/event/Logging.scala
+++ b/akka-actor/src/main/scala/akka/event/Logging.scala
@@ -16,6 +16,7 @@ import scala.concurrent.duration._
 import scala.concurrent.Await
 import scala.util.control.NoStackTrace
 import scala.util.control.NonFatal
+import java.util.Locale
 
 /**
  * This trait brings log level handling to the EventStream: it reads the log
@@ -440,7 +441,7 @@ object Logging {
    * valid inputs are upper or lowercase (not mixed) versions of:
    * "error", "warning", "info" and "debug"
    */
-  def levelFor(s: String): Option[LogLevel] = s.toLowerCase match {
+  def levelFor(s: String): Option[LogLevel] = s.toLowerCase(Locale.ROOT) match {
     case "off"     ⇒ Some(OffLevel)
     case "error"   ⇒ Some(ErrorLevel)
     case "warning" ⇒ Some(WarningLevel)
diff --git a/akka-actor/src/main/scala/akka/util/Helpers.scala b/akka-actor/src/main/scala/akka/util/Helpers.scala
index da4202b9a2..fc7f4e7b4d 100644
--- a/akka-actor/src/main/scala/akka/util/Helpers.scala
+++ b/akka-actor/src/main/scala/akka/util/Helpers.scala
@@ -10,10 +10,11 @@ import com.typesafe.config.Config
 import scala.concurrent.duration.FiniteDuration
 import scala.concurrent.duration.Duration
 import java.util.concurrent.TimeUnit
+import java.util.Locale
 
 object Helpers {
 
-  val isWindows: Boolean = System.getProperty("os.name", "").toLowerCase.indexOf("win") >= 0
+  val isWindows: Boolean = System.getProperty("os.name", "").toLowerCase(Locale.ROOT).indexOf("win") >= 0
 
   def makePattern(s: String): Pattern = Pattern.compile("^\\Q" + s.replace("?", "\\E.\\Q").replace("*", "\\E.*\\Q") + "\\E$")
 
diff --git a/akka-cluster/src/main/scala/akka/cluster/ClusterSettings.scala b/akka-cluster/src/main/scala/akka/cluster/ClusterSettings.scala
index 04d2e016c0..ad18ab0fba 100644
--- a/akka-cluster/src/main/scala/akka/cluster/ClusterSettings.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/ClusterSettings.scala
@@ -15,6 +15,7 @@ import akka.util.Helpers.Requiring
 import akka.util.Helpers.ConfigOps
 import scala.concurrent.duration.FiniteDuration
 import akka.japi.Util.immutableSeq
+import java.util.Locale
 
 final class ClusterSettings(val config: Config, val systemName: String) {
 
@@ -38,7 +39,7 @@ final class ClusterSettings(val config: Config, val systemName: String) {
   val SeedNodeTimeout: FiniteDuration = cc.getMillisDuration("seed-node-timeout")
   val RetryUnsuccessfulJoinAfter: Duration = {
     val key = "retry-unsuccessful-join-after"
-    cc.getString(key).toLowerCase match {
+    cc.getString(key).toLowerCase(Locale.ROOT) match {
       case "off" ⇒ Duration.Undefined
       case _     ⇒ cc.getMillisDuration(key) requiring (_ > Duration.Zero, key + " > 0s, or off")
     }
@@ -52,7 +53,7 @@ final class ClusterSettings(val config: Config, val systemName: String) {
   val UnreachableNodesReaperInterval: FiniteDuration = cc.getMillisDuration("unreachable-nodes-reaper-interval")
   val PublishStatsInterval: Duration = {
     val key = "publish-stats-interval"
-    cc.getString(key).toLowerCase match {
+    cc.getString(key).toLowerCase(Locale.ROOT) match {
       case "off" ⇒ Duration.Undefined
       case _     ⇒ cc.getMillisDuration(key) requiring (_ >= Duration.Zero, key + " >= 0s, or off")
     }
@@ -60,7 +61,7 @@ final class ClusterSettings(val config: Config, val systemName: String) {
 
   val AutoDownUnreachableAfter: Duration = {
     val key = "auto-down-unreachable-after"
-    cc.getString(key).toLowerCase match {
+    cc.getString(key).toLowerCase(Locale.ROOT) match {
       case "off" ⇒ Duration.Undefined
       case _     ⇒ cc.getMillisDuration(key) requiring (_ >= Duration.Zero, key + " >= 0s, or off")
     }
diff --git a/akka-remote/src/main/scala/akka/remote/RemoteSettings.scala b/akka-remote/src/main/scala/akka/remote/RemoteSettings.scala
index 4040ca8009..d1dcf0fd0c 100644
--- a/akka-remote/src/main/scala/akka/remote/RemoteSettings.scala
+++ b/akka-remote/src/main/scala/akka/remote/RemoteSettings.scala
@@ -15,6 +15,7 @@ import akka.actor.Props
 import akka.event.Logging
 import akka.event.Logging.LogLevel
 import akka.ConfigurationException
+import java.util.Locale
 
 final class RemoteSettings(val config: Config) {
   import config._
@@ -29,7 +30,7 @@ final class RemoteSettings(val config: Config) {
   val TrustedSelectionPaths: Set[String] =
     immutableSeq(getStringList("akka.remote.trusted-selection-paths")).toSet
 
-  val RemoteLifecycleEventsLogLevel: LogLevel = getString("akka.remote.log-remote-lifecycle-events").toLowerCase() match {
+  val RemoteLifecycleEventsLogLevel: LogLevel = getString("akka.remote.log-remote-lifecycle-events").toLowerCase(Locale.ROOT) match {
     case "on" ⇒ Logging.DebugLevel
     case other ⇒ Logging.levelFor(other) match {
       case Some(level) ⇒ level