diff --git a/src/main/scala/com/signalcollect/util/IteratorConcatenator.scala b/src/main/scala/com/signalcollect/util/IteratorConcatenator.scala
new file mode 100644
index 00000000..d648b6ca
--- /dev/null
+++ b/src/main/scala/com/signalcollect/util/IteratorConcatenator.scala
@@ -0,0 +1,59 @@
+/*
+ *  @author Philip Stutz
+ *
+ *  Copyright 2014 University of Zurich
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ */
+
+package com.signalcollect.util
+
+import scala.annotation.tailrec
+import scala.collection.mutable.Queue
+
+/**
+ * To avoid https://issues.scala-lang.org/browse/SI-8428, which is not really fixed.
+ * 
+ * Unfortunately I could not reproduce the problem outside of a large and complex TripleRush evaluation.
+ */
+final class IteratorConcatenator[U] extends Iterator[U] {
+
+  val iterators = new Queue[Iterator[U]]()
+
+  def clear {
+    iterators.clear
+  }
+
+  def appendIterator(i: Iterator[U]) {
+    iterators.enqueue(i)
+  }
+
+  def next: U = {
+    iterators.head.next
+  }
+
+  @tailrec def hasNext: Boolean = {
+    if (iterators.isEmpty) {
+      false
+    } else {
+      val headHasNext = iterators.head.hasNext
+      if (!headHasNext) {
+        iterators.dequeue
+        hasNext
+      } else {
+        true
+      }
+    }
+  }
+}
diff --git a/src/main/scala/com/signalcollect/worker/WorkerImplementation.scala b/src/main/scala/com/signalcollect/worker/WorkerImplementation.scala
index 9adaacdc..b5cecc09 100755
--- a/src/main/scala/com/signalcollect/worker/WorkerImplementation.scala
+++ b/src/main/scala/com/signalcollect/worker/WorkerImplementation.scala
@@ -26,11 +26,11 @@ import java.io.File
 import java.io.FileInputStream
 import java.io.FileOutputStream
 import java.lang.management.ManagementFactory
-
 import scala.annotation.elidable
 import scala.annotation.elidable.ASSERTION
+import scala.annotation.tailrec
 import scala.util.Random
-
+import scala.collection.mutable.Queue
 import com.signalcollect.Edge
 import com.signalcollect.GraphEditor
 import com.signalcollect.Vertex
@@ -55,9 +55,9 @@ import com.signalcollect.interfaces.WorkerStatistics
 import com.signalcollect.interfaces.WorkerStatus
 import com.signalcollect.serialization.DefaultSerializer
 import com.sun.management.OperatingSystemMXBean
-
 import akka.actor.ActorRef
 import akka.event.LoggingAdapter
+import com.signalcollect.util.IteratorConcatenator
 
 /**
  * Main implementation of the WorkerApi interface.
@@ -80,6 +80,7 @@ class WorkerImplementation[@specialized(Int, Long) Id, Signal](
   var collectThreshold: Double)
   extends Worker[Id, Signal] {
 
+  val pendingModifications = new IteratorConcatenator[GraphEditor[Id, Signal] => Unit]()
   val workersPerNode = numberOfWorkers / numberOfNodes // Assumes that there is the same number of workers on all nodes.
   val nodeId = getNodeId(workerId)
   val pingPongSchedulingIntervalInMilliseconds = 4 // schedule pingpong exchange every 8ms
@@ -98,7 +99,6 @@ class WorkerImplementation[@specialized(Int, Long) Id, Signal](
   var allWorkDoneWhenContinueSent: Boolean = _
   var lastStatusUpdate: Long = _
   var vertexStore: Storage[Id, Signal] = _
-  var pendingModifications: Iterator[GraphEditor[Id, Signal] => Unit] = _
   var pingSentTimestamp: Long = _
   var pingPongScheduled: Boolean = _
   var waitingForPong: Boolean = _
@@ -118,7 +118,7 @@ class WorkerImplementation[@specialized(Int, Long) Id, Signal](
     allWorkDoneWhenContinueSent = false
     lastStatusUpdate = System.currentTimeMillis
     vertexStore = storageFactory.createInstance
-    pendingModifications = Iterator.empty
+    pendingModifications.clear
     pingSentTimestamp = 0
     pingPongScheduled = false
     waitingForPong = false
@@ -364,7 +364,7 @@ class WorkerImplementation[@specialized(Int, Long) Id, Signal](
   }
 
   override def loadGraph(graphModifications: Iterator[GraphEditor[Id, Signal] => Unit], vertexIdHint: Option[Id]) {
-    pendingModifications = new IteratorConcatenator(pendingModifications, graphModifications) // To avoid https://issues.scala-lang.org/browse/SI-8428, which is not really fixed.
+    pendingModifications.appendIterator(graphModifications) // To avoid https://issues.scala-lang.org/browse/SI-8428, which is not really fixed.
   }
 
   override def setSignalThreshold(st: Double) {
@@ -724,54 +724,3 @@ trait WorkerInterceptor[Id, Signal] extends WorkerApi[Id, Signal] {
     super.deleteSnapshot
   }
 }
-
-class IteratorConcatenator[U](private var a: Iterator[U], private var b: Iterator[U]) extends Iterator[U] { // To avoid https://issues.scala-lang.org/browse/SI-8428, which is not really fixed.
-
-  a = simplify(a)
-  b = simplify(b)
-
-  def simplify(i: Iterator[U]): Iterator[U] = if (i.isInstanceOf[IteratorConcatenator[U]]) {
-    val iCast = i.asInstanceOf[IteratorConcatenator[U]]
-    if (iCast.a == null || !iCast.a.hasNext) {
-      if (iCast.b == null || !iCast.b.hasNext) {
-        null.asInstanceOf[Iterator[U]]
-      } else {
-        iCast.b
-      }
-    } else if (iCast.b == null || !iCast.b.hasNext) {
-      iCast.a
-    } else {
-      iCast
-    }
-  } else {
-    i
-  }
-
-  def next: U = if (a != null) {
-    a.next
-  } else {
-    b.next
-  }
-
-  def hasNext: Boolean = {
-    if (a != null) {
-      val aGotMore = a.hasNext
-      if (!aGotMore) {
-        a = null
-        hasNext
-      } else {
-        true
-      }
-    } else if (b != null) {
-      val bGotMore = b.hasNext
-      if (!bGotMore) {
-        b = null
-        false
-      } else {
-        true
-      }
-    } else {
-      false
-    }
-  }
-}
diff --git a/src/test/scala/com/signalcollect/util/IteratorConcatenatorSpec.scala b/src/test/scala/com/signalcollect/util/IteratorConcatenatorSpec.scala
new file mode 100755
index 00000000..7d89e587
--- /dev/null
+++ b/src/test/scala/com/signalcollect/util/IteratorConcatenatorSpec.scala
@@ -0,0 +1,54 @@
+/*
+ *  @author Philip Stutz
+ *
+ *  Copyright 2014 University of Zurich
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package com.signalcollect.util
+
+import org.scalacheck.Gen
+import org.scalacheck.Gen._
+import org.scalacheck.Arbitrary._
+import org.scalatest.FlatSpec
+import org.scalatest.ShouldMatchers
+import org.scalatest.prop.Checkers
+import java.io.DataOutputStream
+import java.io.ByteArrayOutputStream
+import org.scalacheck.Arbitrary
+
+class IteratorConcatenatorSpec extends FlatSpec with ShouldMatchers with Checkers with TestAnnouncements {
+
+  "IteratorConcatenator" should "correctly concatenate multiple iterators" in {
+    val c = new IteratorConcatenator[Int]
+    for (i <- 1 to 1000 by 10) {
+      c.appendIterator((i until i + 10).iterator)
+    }
+    c.appendIterator(Seq(1001, 1002, 1003).iterator)
+    c.appendIterator(Set(1004).iterator)
+    assert(c.toList == (1 to 1004).toList)
+  }
+
+  it should "should work with random appends" in {
+    check(
+      (is: List[List[Int]]) => {
+        val c = new IteratorConcatenator[Int]
+        is.foreach { list => c.appendIterator(list.iterator) }
+        assert(c.toList == is.flatMap(_.iterator).toList)
+        true
+      },
+      minSuccessful(100))
+  }
+
+}