2 files changed, 64 insertions, 10 deletions
diff --git a/src/actors/scala/actors/Actor.scala b/src/actors/scala/actors/Actor.scala
index 25cfbf7865..57e107538c 100644
--- a/src/actors/scala/actors/Actor.scala
+++ b/src/actors/scala/actors/Actor.scala
@@ -590,20 +590,27 @@ trait Actor extends AbstractActor with ReplyReactor with ActorCanReply with Inpu
             receiveTimeout
           } else {
             if (onTimeout.isEmpty) {
-              waitingFor = f
-              received = None
-              isSuspended = true
+              if (!f.isDefinedAt(TIMEOUT))
+                sys.error("unhandled timeout")
+
               val thisActor = this
               onTimeout = Some(new TimerTask {
-                def run() { thisActor.send(TIMEOUT, thisActor) }
+                def run() {
+                  thisActor.send(TIMEOUT, thisActor)
+                }
               })
               Actor.timer.schedule(onTimeout.get, msec)
-              scheduler.managedBlock(blocker)
-              drainSendBuffer(mailbox)
-              // keep going
-              () => {}
-            } else
-              sys.error("unhandled timeout")
+            }
+
+            // It is possible that !onTimeout.isEmpty, but TIMEOUT is not yet in mailbox
+            // See SI-4759
+            waitingFor = f
+            received = None
+            isSuspended = true
+            scheduler.managedBlock(blocker)
+            drainSendBuffer(mailbox)
+            // keep going
+            () => {}
           }
         }
         todo()
diff --git a/test/files/jvm/actor-sync-send-timeout.scala b/test/files/jvm/actor-sync-send-timeout.scala
new file mode 100644
index 0000000000..ed330900b2
--- /dev/null
+++ b/test/files/jvm/actor-sync-send-timeout.scala
@@ -0,0 +1,47 @@
+import scala.actors.Actor
+
+/* This test is a regression test for SI-4759.
+ */
+object Test {
+  val Runs = 5
+
+  def main(args: Array[String]) = {
+    var i = 0
+    while (i < Runs) {
+      i += 1
+      A1 ! 1
+      Thread.sleep(500)
+    }
+    //println("done sending to A1")
+  }
+}
+
+object A2 extends Actor {
+  this.start()
+  def act() {
+    loop {
+      react {
+        case 'stop =>
+          //println("A2 exiting")
+          exit()
+        case _ =>
+      }
+    }
+  }
+}
+
+object A1 extends Actor {
+  this.start()
+  def act() {
+    var i = 0
+    loopWhile(i < Test.Runs) {
+      i += 1
+      react {
+        case any =>
+          A2 !? (500, any)
+          if (i == Test.Runs)
+            A2 ! 'stop
+      }
+    }
+  }
+}