diff --git a/akka-actor-tests/src/test/scala/akka/util/ByteStringSpec.scala b/akka-actor-tests/src/test/scala/akka/util/ByteStringSpec.scala
index 1e2fce7b4c..1514635c8a 100644
--- a/akka-actor-tests/src/test/scala/akka/util/ByteStringSpec.scala
+++ b/akka-actor-tests/src/test/scala/akka/util/ByteStringSpec.scala
@@ -21,11 +21,7 @@ import scala.collection.mutable.Builder
 
 class ByteStringSpec extends WordSpec with Matchers with Checkers {
 
-  //  // uncomment when developing locally to get better coverage
-  //  implicit override val generatorDrivenConfig =
-  //    PropertyCheckConfig(
-  //      minSuccessful = 1000,
-  //      minSize = 0, maxSize = 100)
+  implicit val betterGeneratorDrivenConfig = PropertyCheckConfig().copy(minSuccessful = 1000)
 
   def genSimpleByteString(min: Int, max: Int) = for {
     n ← Gen.choose(min, max)
@@ -365,13 +361,48 @@ class ByteStringSpec extends WordSpec with Matchers with Checkers {
       ByteStrings(ByteString1.fromString(""), ByteString1.fromString("ab")).dropRight(Int.MinValue) should ===(ByteString("ab"))
     }
     "slice" in {
-      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(0, 1) should ===(ByteString("a"))
       ByteStrings(ByteString1.fromString(""), ByteString1.fromString("a")).slice(1, 1) should ===(ByteString(""))
+      // We explicitly test all edge cases to always test them, refs bug #21237
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(-10, 10) should ===(ByteString("a"))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(-10, 0) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(-10, 1) should ===(ByteString("a"))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(0, 1) should ===(ByteString("a"))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(0, 10) should ===(ByteString("a"))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(1, 10) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(1, -2) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(-10, -100) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(-100, -10) should ===(ByteString(""))
+      // Get an empty if `from` is greater then `until`
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(1, 0) should ===(ByteString(""))
+
       ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(2, 2) should ===(ByteString(""))
       ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(2, 3) should ===(ByteString("c"))
       ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(2, 4) should ===(ByteString("cd"))
       ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(3, 4) should ===(ByteString("d"))
-      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(10, 100) should ===(ByteString(""))
+      // Can obtain expected results from 6 basic patterns
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(-10, 10) should ===(ByteString("abcd"))
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(-10, 0) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(-10, 4) should ===(ByteString("abcd"))
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(0, 4) should ===(ByteString("abcd"))
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(1, -2) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(0, 10) should ===(ByteString("abcd"))
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(-10, -100) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(-100, -10) should ===(ByteString(""))
+
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(1, -2) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(-10, -100) should ===(ByteString(""))
+      ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).slice(-100, -10) should ===(ByteString(""))
+
+      // various edge cases using raw ByteString1
+      ByteString1.fromString("cd").slice(100, 10) should ===(ByteString(""))
+      ByteString1.fromString("cd").slice(100, 1000) should ===(ByteString(""))
+      ByteString1.fromString("cd").slice(-10, -5) should ===(ByteString(""))
+      ByteString1.fromString("cd").slice(-2, -5) should ===(ByteString(""))
+      ByteString1.fromString("cd").slice(-2, 1) should ===(ByteString("c"))
+      ByteString1.fromString("abcd").slice(1, -1) should ===(ByteString(""))
+
+      // Get an empty if `from` is greater than `until`
+      ByteStrings(ByteString1.fromString("ab"), ByteString1.fromString("cd")).slice(4, 0) should ===(ByteString(""))
     }
     "dropRight" in {
       ByteStrings(ByteString1.fromString("a"), ByteString1.fromString("")).dropRight(0) should ===(ByteString("a"))
diff --git a/akka-actor/src/main/scala/akka/util/ByteString.scala b/akka-actor/src/main/scala/akka/util/ByteString.scala
index 6438d95c48..0b07bbdcc5 100644
--- a/akka-actor/src/main/scala/akka/util/ByteString.scala
+++ b/akka-actor/src/main/scala/akka/util/ByteString.scala
@@ -163,8 +163,8 @@ object ByteString {
       else toByteString1.drop(n)
 
     override def slice(from: Int, until: Int): ByteString =
-      if ((from == 0) && (until == length)) this
-      else if (from > length) ByteString.empty
+      if (from <= 0 && until >= length) this
+      else if (from >= length || until <= 0 || from >= until) ByteString.empty
       else toByteString1.slice(from, until)
 
     private[akka] override def writeToOutputStream(os: ObjectOutputStream): Unit =
@@ -252,11 +252,8 @@ object ByteString {
       if (n <= 0) ByteString.empty
       else ByteString1(bytes, startIndex, Math.min(n, length))
 
-    override def slice(from: Int, until: Int): ByteString = {
-      if (from <= 0 && until >= length) this // we can do < / > since we're Compact
-      else if (until <= from) ByteString1.empty
-      else ByteString1(bytes, startIndex + from, until - from)
-    }
+    override def slice(from: Int, until: Int): ByteString =
+      drop(from).take(until - Math.max(0, from))
 
     override def copyToBuffer(buffer: ByteBuffer): Int =
       writeToBuffer(buffer)
@@ -466,7 +463,7 @@ object ByteString {
       }
 
     override def slice(from: Int, until: Int): ByteString =
-      if ((from == 0) && (until == length)) this
+      if (from <= 0 && until >= length) this
       else if (from > length || until <= from) ByteString.empty
       else drop(from).dropRight(length - until)