diff --git a/core/src/main/java/hudson/model/Computer.java b/core/src/main/java/hudson/model/Computer.java
index 05ec1925a2de409792ba7c4bcda929b115960739..e3c95d7a380518395c1c860bb438c0121b53b114 100644
--- a/core/src/main/java/hudson/model/Computer.java
+++ b/core/src/main/java/hudson/model/Computer.java
@@ -269,6 +269,17 @@ public abstract class Computer extends AbstractModelObject {
         return true;
     }
 
+    /**
+     * Returns the time when this computer first became idle.
+     */
+    public final long getIdleStartMilliseconds() {
+        long firstIdle = Long.MIN_VALUE;
+        for (Executor e : executors) {
+            firstIdle = Math.max(firstIdle, e.getIdleStartMilliseconds());
+        }
+        return firstIdle;
+    }
+
     /**
      * Called by {@link Executor} to kill excessive executors from this computer.
      */
diff --git a/core/src/main/java/hudson/model/Executor.java b/core/src/main/java/hudson/model/Executor.java
index 2b295587c33e00b76ffd7e78e66d3a43ac329379..57939aea23735952341841533269f9a22d1e6774 100644
--- a/core/src/main/java/hudson/model/Executor.java
+++ b/core/src/main/java/hudson/model/Executor.java
@@ -22,6 +22,10 @@ public class Executor extends Thread implements ModelObject {
     private final Queue queue;
 
     private long startTime;
+    /**
+     * Used to track when a job was last executed.
+     */
+    private long finishTime;
 
     /**
      * Executor number that identifies it among other executors for the same {@link Computer}.
@@ -47,6 +51,7 @@ public class Executor extends Thread implements ModelObject {
         SecurityContextHolder.getContext().setAuthentication(ACL.SYSTEM);
 
         try {
+            finishTime = System.currentTimeMillis();
             while(true) {
                 if(Hudson.getInstance().isTerminating())
                     return;
@@ -81,6 +86,7 @@ public class Executor extends Thread implements ModelObject {
                     // so just leave some info and go on to build other things
                     LOGGER.log(Level.SEVERE, "Executor throw an exception unexpectedly",e);
                 }
+                finishTime = System.currentTimeMillis();
                 executable = null;
             }
         } catch(RuntimeException e) {
@@ -195,6 +201,18 @@ public class Executor extends Thread implements ModelObject {
         return owner;
     }
 
+    /**
+     * Returns when this executor started or should start being idle.
+     */
+    public long getIdleStartMilliseconds() {
+        if (isIdle())
+            return finishTime;
+        else {
+            return Math.max(startTime + executable.getParent().getEstimatedDuration(),
+                    System.currentTimeMillis() + 15000);
+        }
+    }
+
     /**
      * Returns the executor of the current thread.
      */
diff --git a/core/src/main/java/hudson/slaves/RetentionStrategy.java b/core/src/main/java/hudson/slaves/RetentionStrategy.java
index e68d4f4c685b57cb5db506168e5d952caadcf773..ee6cf75da1b73768db3617efaa7576325da90cd5 100644
--- a/core/src/main/java/hudson/slaves/RetentionStrategy.java
+++ b/core/src/main/java/hudson/slaves/RetentionStrategy.java
@@ -117,9 +117,6 @@ public abstract class RetentionStrategy<T extends Computer> implements Describab
          */
         private final long idleDelay;
 
-        private transient Long finishTransition = null;
-        private transient Boolean startState = null;
-
         @DataBoundConstructor
         public Demand(long inDemandDelay, long idleDelay) {
             this.inDemandDelay = inDemandDelay;
@@ -150,55 +147,31 @@ public abstract class RetentionStrategy<T extends Computer> implements Describab
          * {@inheritDoc}
          */
         public synchronized long check(SlaveComputer c) {
-            if (!Boolean.valueOf(c.isOffline()).equals(startState)) {
-                // reset the timer as we are no longer in the starting state
-                finishTransition = null;
-                startState = c.isOffline();
-            }
             if (c.isOffline()) {
                 final Queue queue = Hudson.getInstance().getQueue();
                 final Queue.Item[] items = queue.getItems(); // TODO filter this array to this computer
                 for (Queue.Item item : items) {
                     if ((System.currentTimeMillis() - item.timestamp.getTimeInMillis()) >
                             TimeUnit.MILLISECONDS.convert(inDemandDelay, TimeUnit.MINUTES)) {
-
-                        logger.log(Level.INFO, "Trying to launch computer {0} as it has been in demand for too long", c.getNode().getNodeName());
                         // we've been in demand for long enough
+                        logger.log(Level.INFO, "Trying to launch computer {0} as it has been in demand for too long", c.getNode().getNodeName());
                         if (c.isOffline() && c.isLaunchSupported())
                             c.tryReconnect();
-                        finishTransition = null;
 
                         break;
                     }
                 }
             } else {
                 if (c.isIdle()) {
-                    if (finishTransition == null) {
-                        logger.log(Level.INFO, "Computer {0} is now idle, {1} minutes until disconnection",
-                                new Object[]{c.getNode().getNodeName(), idleDelay});
-                        // only just noticed that we're idle
-                        finishTransition = System.currentTimeMillis() +
-                                TimeUnit.MILLISECONDS.convert(idleDelay, TimeUnit.MINUTES);
-                    } else if (System.currentTimeMillis() > finishTransition) {
-                        logger.log(Level.INFO, "Disconnecting computer {0} as it has been idle too long", c.getNode().getNodeName());
+                    if (System.currentTimeMillis() - c.getIdleStartMilliseconds() >
+                            TimeUnit.MILLISECONDS.convert(inDemandDelay, TimeUnit.MINUTES)) {
                         // we've been idle for long enough
+                        logger.log(Level.INFO, "Disconnecting computer {0} as it has been idle too long", c.getNode().getNodeName());
                         c.disconnect();
-                        finishTransition = null;
-                    } else {
-                        logger.log(Level.INFO, "Computer {0} is still idle, {1} minutes until disconnection",
-                                new Object[]{c.getNode().getNodeName(),
-                                        TimeUnit.MILLISECONDS.convert(
-                                                Math.max(0, finishTransition - System.currentTimeMillis()),
-                                                TimeUnit.MINUTES)
-                                });
                     }
-                } else {
-                    // reset our timer
-                    finishTransition = null;
                 }
-                return 1;
             }
-            return 0;
+            return 1;
         }
 
         /**