diff --git a/src/Handler/Utils/Exam.hs b/src/Handler/Utils/Exam.hs
index cfb4124c2..097ff62f1 100644
--- a/src/Handler/Utils/Exam.hs
+++ b/src/Handler/Utils/Exam.hs
@@ -311,14 +311,13 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
 
     occurrences' :: Map ExamOccurrenceId Natural
     -- ^ reduce room capacity for every pre-assigned user by 1
-    occurrences' = foldl' (flip $ Map.update predToPositive) occurrences $ Map.mapMaybe snd users
-    -- FIXME what about capacity-0 in occurrences?
-    -- what if the first word is too big for the first room?
-      where
-        predToPositive :: Natural -> Maybe Natural
-        predToPositive 0 = Nothing
-        predToPositive 1 = Nothing
-        predToPositive n = Just $ pred n
+    -- also remove empty/pre-filled rooms
+    occurrences' = foldl' (flip $ Map.update predToPositive) (Map.filter (> 0) occurrences) $ Map.mapMaybe snd users
+
+    predToPositive :: Natural -> Maybe Natural
+    predToPositive 0 = Nothing
+    predToPositive 1 = Nothing
+    predToPositive n = Just $ pred n
 
     occurrences'' :: [(ExamOccurrenceId, Natural)]
     -- ^ Minimise number of occurrences used