diff --git a/core/src/main/scala/com/phaller/rasync/HandlerPool.scala b/core/src/main/scala/com/phaller/rasync/HandlerPool.scala
index 595f279..4a1a24f 100644
--- a/core/src/main/scala/com/phaller/rasync/HandlerPool.scala
+++ b/core/src/main/scala/com/phaller/rasync/HandlerPool.scala
@@ -12,10 +12,17 @@ import lattice.{ DefaultKey, Key, Updater }
 import org.opalj.graphs._
 
 import scala.collection.immutable.Queue
+import scala.util.{ Success, Try }
 
 /* Need to have reference equality for CAS.
+ *
+ * quiescenceCellHandlers use NEXTCallbackRunnable, because (a) pool might reach quiescence
+ * repeatedly and (b) cell might not be completed, when quiescence is reached.
  */
-private class PoolState(val handlers: List[() => Unit] = List(), val submittedTasks: Int = 0) {
+private class PoolState(
+  val quiescenceHandlers: List[() => Unit] = List(),
+  val quiescenceCellHandlers: List[NextCallbackRunnable[_, _]] = List(),
+  val submittedTasks: Int = 0) {
   def isQuiescent(): Boolean =
     submittedTasks == 0
 }
@@ -63,13 +70,27 @@ class HandlerPool(parallelism: Int = 8, unhandledExceptionHandler: Throwable =>
     if (state.isQuiescent) {
       execute(new Runnable { def run(): Unit = handler() })
     } else {
-      val newState = new PoolState(handler :: state.handlers, state.submittedTasks)
+      val newState = new PoolState(handler :: state.quiescenceHandlers, state.quiescenceCellHandlers, state.submittedTasks)
       val success = poolState.compareAndSet(state, newState)
       if (!success)
         onQuiescent(handler)
     }
   }
 
+  @tailrec
+  final def onQuiescent[K <: Key[V], V](cell: Cell[K, V])(handler: Try[V] => Unit): Unit = {
+    val state = poolState.get()
+    if (state.isQuiescent) {
+      execute(new Runnable { def run(): Unit = handler(Success(cell.getResult())) })
+    } else {
+      val runnable = new NextConcurrentCallbackRunnable(this, null, cell, handler)
+      val newState = new PoolState(state.quiescenceHandlers, runnable :: state.quiescenceCellHandlers, state.submittedTasks)
+      val success = poolState.compareAndSet(state, newState)
+      if (!success)
+        onQuiescent(cell)(handler)
+    }
+  }
+
   /**
    * Register a cell with this HandlerPool.
    *
@@ -265,7 +286,7 @@ class HandlerPool(parallelism: Int = 8, unhandledExceptionHandler: Throwable =>
     var submitSuccess = false
     while (!submitSuccess) {
       val state = poolState.get()
-      val newState = new PoolState(state.handlers, state.submittedTasks + 1)
+      val newState = new PoolState(state.quiescenceHandlers, state.quiescenceCellHandlers, state.submittedTasks + 1)
       submitSuccess = poolState.compareAndSet(state, newState)
     }
   }
@@ -281,10 +302,10 @@ class HandlerPool(parallelism: Int = 8, unhandledExceptionHandler: Throwable =>
       val state = poolState.get()
       if (state.submittedTasks > i) {
         handlersToRun = None
-        val newState = new PoolState(state.handlers, state.submittedTasks - i)
+        val newState = new PoolState(state.quiescenceHandlers, state.quiescenceCellHandlers, state.submittedTasks - i)
         success = poolState.compareAndSet(state, newState)
       } else if (state.submittedTasks == 1) {
-        handlersToRun = Some(state.handlers)
+        handlersToRun = Some(state.quiescenceHandlers)
         val newState = new PoolState()
         success = poolState.compareAndSet(state, newState)
       } else {
diff --git a/core/src/test/scala/com/phaller/rasync/test/pool.scala b/core/src/test/scala/com/phaller/rasync/test/pool.scala
index 741f6ab..f8faea6 100644
--- a/core/src/test/scala/com/phaller/rasync/test/pool.scala
+++ b/core/src/test/scala/com/phaller/rasync/test/pool.scala
@@ -1,13 +1,15 @@
 package com.phaller.rasync
 package test
 
-import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.{ ConcurrentHashMap, CountDownLatch }
 
 import org.scalatest.FunSuite
 
 import scala.concurrent.{ Await, Promise }
 import scala.concurrent.duration._
-import lattice.{ Lattice, StringIntKey, StringIntUpdater, Updater }
+
+import scala.util.{ Failure, Success }
+import lattice.{ StringIntKey, StringIntUpdater, Updater }
 
 class PoolSuite extends FunSuite {
   test("onQuiescent") {
@@ -69,4 +71,70 @@ class PoolSuite extends FunSuite {
     assert(regCells.size === 1000)
   }
 
+  test("onQuiescent(cell): incomplete cell") {
+    val latch = new CountDownLatch(1)
+
+    val pool = new HandlerPool
+    val completer1 = CellCompleter[StringIntKey, Int]("somekey")(new StringIntUpdater, pool)
+
+    var i = 0
+    while (i < 10000) {
+      val p1 = Promise[Boolean]()
+      val p2 = Promise[Boolean]()
+      pool.execute { () => { p1.success(true); () } }
+      pool.onQuiescent { () => p2.success(true) }
+      try {
+        Await.result(p2.future, 1.seconds)
+      } catch {
+        case t: Throwable =>
+          assert(false, s"failure after $i iterations")
+      }
+      i += 1
+    }
+
+    pool.onQuiescent(completer1.cell) {
+      case Success(x) =>
+        assert(x === 0)
+        latch.countDown()
+      case Failure(_) => assert(false)
+    }
+
+    latch.await()
+
+    pool.shutdown()
+  }
+
+  test("onQuiescent(cell): completed cell") {
+    val latch = new CountDownLatch(1)
+
+    val pool = new HandlerPool
+    val completer1 = CellCompleter.completed[Int](10)(new StringIntUpdater, pool)
+
+    var i = 0
+    while (i < 10000) {
+      val p1 = Promise[Boolean]()
+      val p2 = Promise[Boolean]()
+      pool.execute { () => { p1.success(true); () } }
+      pool.onQuiescent { () => p2.success(true) }
+      try {
+        Await.result(p2.future, 1.seconds)
+      } catch {
+        case t: Throwable =>
+          assert(false, s"failure after $i iterations")
+      }
+      i += 1
+    }
+
+    pool.onQuiescent(completer1.cell) {
+      case Success(x) =>
+        assert(x === 10)
+        latch.countDown()
+      case Failure(_) => assert(false)
+    }
+
+    latch.await()
+
+    pool.shutdown()
+  }
+
 }