diff --git a/akka-actor/src/main/scala/akka/actor/ActorSystem.scala b/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
index 721375adda..0483ccf60f 100644
--- a/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
+++ b/akka-actor/src/main/scala/akka/actor/ActorSystem.scala
@@ -430,7 +430,7 @@ private[akka] class ActorSystemImpl(val name: String, applicationConfig: Config,
   if (!name.matches("""^[a-zA-Z0-9][a-zA-Z0-9-]*$"""))
     throw new IllegalArgumentException(
       "invalid ActorSystem name [" + name +
-        "], must contain only word characters (i.e. [a-zA-Z_0-9] plus non-leading '-')")
+        "], must contain only word characters (i.e. [a-zA-Z0-9] plus non-leading '-')")
 
   import ActorSystem._