diff --git a/pyerrors/input/hadrons.py b/pyerrors/input/hadrons.py
index 41b437a2..e9097625 100644
--- a/pyerrors/input/hadrons.py
+++ b/pyerrors/input/hadrons.py
@@ -45,9 +45,11 @@ def _get_files(path, filestem, idl):
         raise Exception("Unsorted files")
     if len(dc) == 1:
         idx = range(cnfg_numbers[0], cnfg_numbers[-1] + dc[0], dc[0])
-    else:
+    elif idl:
         idx = idl
         warnings.warn("Configurations are not evenly spaced.", RuntimeWarning)
+    else:
+        raise Exception("Configurations are not evenly spaced.")
 
     return filtered_files, idx