diff --git a/analysis/tasks/Warmup.py b/analysis/tasks/Warmup.py
index b8ef797d088c73383f84ae0853e38da0cffccbe6..636a61a632d6dfebf3938d8a428e785b9ab3e84d 100644
--- a/analysis/tasks/Warmup.py
+++ b/analysis/tasks/Warmup.py
@@ -36,7 +36,7 @@ class Warmup(Task, TarballExtractionMixin, HTCondorWorkflow, law.LocalWorkflow):
     warmup_iterations = SpaceSeparatedListParameter(cls=luigi.IntParameter)
 
     NNLOJET_RUNMODE   = 'warmup'
-    NNLOJET_UNITPHASE = ''
+    NNLOJET_UNITPHASE = '! UNIT_PHASE'
 
     # NNLOJET frequently does NOT report errors properly (return code > 0)!
     # ==> scan stdout for these strings to check if an error occurred