diff --git a/akka-actor/src/main/scala/akka/util/Helpers.scala b/akka-actor/src/main/scala/akka/util/Helpers.scala
index ef23c1d712..830ec28881 100644
--- a/akka-actor/src/main/scala/akka/util/Helpers.scala
+++ b/akka-actor/src/main/scala/akka/util/Helpers.scala
@@ -29,7 +29,7 @@ object Helpers {
     def compare(a: AnyRef, b: AnyRef): Int = compareIdentityHash(a, b)
   }
 
-  final val base64chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789*?"
+  final val base64chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+%"
 
   @tailrec
   def base64(l: Long, sb: StringBuilder = new StringBuilder("$")): String = {