diff --git a/src/Handler/Utils/Exam.hs b/src/Handler/Utils/Exam.hs
index 596700220..9a63a6ac3 100644
--- a/src/Handler/Utils/Exam.hs
+++ b/src/Handler/Utils/Exam.hs
@@ -45,6 +45,7 @@ import qualified Data.Array as Array
 import Data.Array.ST (STArray, STUArray)
 import qualified Data.Array.ST as ST
 
+import Data.Foldable (foldMap')
 import Data.List (findIndex, unfoldr)
 import qualified Data.List as List
 
@@ -392,7 +393,7 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
         | otherwise -> Map.singleton [] $ Map.keysSet users
 
     occurrencesSize :: ExamOccurrenceCapacity
-    occurrencesSize = fold occurrences'
+    occurrencesSize = foldMap' (view _2) occurrences''
 
     occurrences' :: Map ExamOccurrenceId ExamOccurrenceCapacity
     -- ^ reduce room capacity for every pre-assigned user by 1