diff --git a/src/xfel_calibrate/calibrate.py b/src/xfel_calibrate/calibrate.py
index 64b2a5806c560e991bfabc88f40160088ca6ba94..cd6b2408409ca436fd06f04c1bed98e4fb93aa57 100755
--- a/src/xfel_calibrate/calibrate.py
+++ b/src/xfel_calibrate/calibrate.py
@@ -717,7 +717,7 @@ class SlurmOptions:
         launcher_slurm += ["--job-name", self.job_name]
 
         if self.nice:
-            launcher_slurm += ["--nice", str(self.nice)]
+            launcher_slurm.append(f"--nice={self.nice}")
 
         if self.mem:
             launcher_slurm.append(f"--mem={self.mem}G")