diff --git a/server/src/main/java/org/elasticsearch/common/util/concurrent/QueueResizingEsThreadPoolExecutor.java b/server/src/main/java/org/elasticsearch/common/util/concurrent/QueueResizingEsThreadPoolExecutor.java
index 14d1ad5b64638..983e4cf206b34 100644
--- a/server/src/main/java/org/elasticsearch/common/util/concurrent/QueueResizingEsThreadPoolExecutor.java
+++ b/server/src/main/java/org/elasticsearch/common/util/concurrent/QueueResizingEsThreadPoolExecutor.java
@@ -151,8 +151,14 @@ protected void afterExecute(Runnable r, Throwable t) {
         final long totalNanos = totalTaskNanos.addAndGet(taskNanos);
 
         final long taskExecutionNanos = timedRunnable.getTotalExecutionNanos();
-        assert taskExecutionNanos >= 0 : "expected task to always take longer than 0 nanoseconds, got: " + taskExecutionNanos;
-        executionEWMA.addValue(taskExecutionNanos);
+        if (taskExecutionNanos > 0) {
+            executionEWMA.addValue(taskExecutionNanos);
+        } else {
+            // wrapper (e.g. ContextPreservingAbstractRunnable) threw an exception before being able to run this task
+            assert taskExecutionNanos == -1 && timedRunnable.isStarted() == false && t != null :
+                "expected task exceptionally never to have started, but got: "
+                    + taskExecutionNanos + " for " + timedRunnable + " with exception [" + t + "]";
+        }
 
         if (taskCount.incrementAndGet() == this.tasksPerFrame) {
             final long endTimeNs = System.nanoTime();
diff --git a/server/src/main/java/org/elasticsearch/common/util/concurrent/TimedRunnable.java b/server/src/main/java/org/elasticsearch/common/util/concurrent/TimedRunnable.java
index b6b9ef1ad05bf..fe09e903a9193 100644
--- a/server/src/main/java/org/elasticsearch/common/util/concurrent/TimedRunnable.java
+++ b/server/src/main/java/org/elasticsearch/common/util/concurrent/TimedRunnable.java
@@ -39,6 +39,7 @@ class TimedRunnable extends AbstractRunnable implements WrappedRunnable {
     @Override
     public void doRun() {
         try {
+            assert finishTimeNanos == -1 : "task already run: finishTimeNanos=" + finishTimeNanos + " for " + this;
             startTimeNanos = System.nanoTime();
             original.run();
         } finally {
@@ -82,7 +83,6 @@ public boolean isForceExecution() {
      */
     long getTotalNanos() {
         if (finishTimeNanos == -1) {
-            // There must have been an exception thrown, the total time is unknown (-1)
             return -1;
         }
         return Math.max(finishTimeNanos - creationTimeNanos, 1);
@@ -93,8 +93,7 @@ long getTotalNanos() {
      * If the task is still running or has not yet been run, returns -1.
      */
     long getTotalExecutionNanos() {
-        if (startTimeNanos == -1 || finishTimeNanos == -1) {
-            // There must have been an exception thrown, the total time is unknown (-1)
+        if (finishTimeNanos == -1) {
             return -1;
         }
         return Math.max(finishTimeNanos - startTimeNanos, 1);
@@ -105,4 +104,15 @@ public Runnable unwrap() {
         return original;
     }
 
+    @Override
+    public String toString() {
+        return "TimedRunnable{" +
+            "original=" + original +
+            '}';
+    }
+
+    // used by assertions only
+    public boolean isStarted() {
+        return startTimeNanos != 0;
+    }
 }