diff --git a/xfel_calibrate/calibrate.py b/xfel_calibrate/calibrate.py
index eed16c2769b840f7086bd8d88af870bd7b5e5496..ee157996979ccbdc85b2f7f9d8288afc2980f176 100755
--- a/xfel_calibrate/calibrate.py
+++ b/xfel_calibrate/calibrate.py
@@ -487,7 +487,7 @@ def flatten_list(l):
         elif len(l) == 1:
             return '{}'.format(l[0])
         else:
-            return '{}'
+            return ''
     else:
         return str(l)