diff --git a/src/python/TaskWorker/Actions/PreDAG.py b/src/python/TaskWorker/Actions/PreDAG.py
index a1fa998b07..73e1ebbade 100644
--- a/src/python/TaskWorker/Actions/PreDAG.py
+++ b/src/python/TaskWorker/Actions/PreDAG.py
@@ -32,10 +32,10 @@
 import tempfile
 import functools
 import subprocess
+from ast import literal_eval
 
 import classad
 
-from ast import literal_eval
 from WMCore.DataStructs.LumiList import LumiList
 
 from ServerUtilities import getLock, newX509env, MAX_IDLE_JOBS, MAX_POST_JOBS
@@ -69,7 +69,7 @@ def readJobStatus(self):
         #XXX Maybe the status_cache filname should be in a variable in ServerUtilities?
         if not os.path.exists("task_process/status_cache.pkl"):
             return
-        with open("task_process/status_cache.pkl",'rb') as fd:
+        with open("task_process/status_cache.pkl", 'rb') as fd:
             statusCache = pickle.load(fd)
             if not 'nodes' in statusCache:
                 return
@@ -174,9 +174,9 @@ def executeInternal(self, *args):
 
         # need to use user proxy as credential for talking with cmsweb
         config.TaskWorker.cmscert = os.environ.get('X509_USER_PROXY')
-        config.TaskWorker.cmskey  = os.environ.get('X509_USER_PROXY')
+        config.TaskWorker.cmskey = os.environ.get('X509_USER_PROXY')
         config.TaskWorker.envForCMSWEB = newX509env(X509_USER_CERT=config.TaskWorker.cmscert,
-                                                         X509_USER_KEY=config.TaskWorker.cmskey)
+                                                    X509_USER_KEY=config.TaskWorker.cmskey)
 
         # need to get username from classAd to setup for Rucio access
         task_ad = classad.parseOne(open(os.environ['_CONDOR_JOB_AD']))
@@ -208,12 +208,18 @@ def executeInternal(self, *args):
                 sumEventsThr += throughput
                 sumEventsSize += eventsize
                 count += 1
-        eventsThr = sumEventsThr / count
-        eventsSize = sumEventsSize / count
+        if count > 0:
+            eventsThr = sumEventsThr / count
+            eventsSize = sumEventsSize / count
 
         self.logger.info("average throughput for %s jobs: %s evt/s", count, eventsThr)
         self.logger.info("average eventsize for %s jobs: %s bytes", count, eventsSize)
 
+        if eventsThr == 0:
+            retmsg = "Splitting failed because all probe jobs failed or anyhow failed to provide estimates"
+            self.logger.error(retmsg)
+            return 1
+
         maxSize = getattr(config.TaskWorker, 'automaticOutputSizeMaximum', 5 * 1000**3)
         maxEvents = (maxSize / eventsSize) if eventsSize > 0 else 0
 
@@ -268,7 +274,10 @@ def executeInternal(self, *args):
             creator = DagmanCreator(config, crabserver=None, rucioClient=rucioClient)
             with config.TaskWorker.envForCMSWEB:
                 creator.createSubdag(split_result.result, task=task, parent=parent, stage=self.stage)
-            self.submitSubdag('RunJobs{0}.subdag'.format(self.prefix), getattr(config.TaskWorker, 'maxIdle', MAX_IDLE_JOBS), getattr(config.TaskWorker, 'maxPost', MAX_POST_JOBS), self.stage)
+            self.submitSubdag('RunJobs{0}.subdag'.format(self.prefix),
+                              getattr(config.TaskWorker, 'maxIdle', MAX_IDLE_JOBS),
+                              getattr(config.TaskWorker, 'maxPost', MAX_POST_JOBS),
+                              self.stage)
         except TaskWorkerException as e:
             retmsg = "DAG creation failed with:\n{0}".format(e)
             self.logger.error(retmsg)
@@ -333,7 +342,7 @@ def adjustLumisForCompletion(self, task, unprocessed):
         # Now we turn lumis it into something like:
         # lumis=['1, 33, 35, 35, 37, 47, 49, 75, 77, 130, 133, 136','1,45,50,80']
         # which is the format expected by buildLumiMask in the splitting algorithm
-        lumis = [",".join(str(l) for l in functools.reduce(lambda x, y:x + y, missing_compact[run])) for run in runs]
+        lumis = [",".join(str(l) for l in functools.reduce(lambda x, y: x + y, missing_compact[run])) for run in runs]
 
         task['tm_split_args']['runs'] = runs
         task['tm_split_args']['lumis'] = lumis