diff --git a/src/Handler/Utils/Exam.hs b/src/Handler/Utils/Exam.hs
index b54ac379c..3d0068735 100644
--- a/src/Handler/Utils/Exam.hs
+++ b/src/Handler/Utils/Exam.hs
@@ -565,7 +565,7 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
     postprocess result = seq resultAscList (resultAscList, resultUsers)
       where
         maxTagLength :: Int
-        maxTagLength = maybe 0 maximum $ fromNullable $ map (length . snd) result
+        maxTagLength = maybe 0 maximum $ fromNullable $ concatMap (map length . snd) result
 
         rangeAlphabet :: [CI Char]
         rangeAlphabet = case rule of