diff --git a/src/Handler/Submission.hs b/src/Handler/Submission.hs
index 2148f3a28..ca79f978d 100644
--- a/src/Handler/Submission.hs
+++ b/src/Handler/Submission.hs
@@ -264,7 +264,16 @@ makeSubmissionForm cid msmid uploadMode grouping isLecturer prefillUsers = ident
           miButtonAction = miButtonAction' mRoute
 
           postProcess :: Map ListPosition (Either UserEmail UserId, ()) -> Set (Either UserEmail UserId)
-          postProcess = setOf $ folded . _1
+          postProcess valMap
+            | Just maxSize' <- maxSize
+            , fromIntegral maxSize' >= Set.size resultUsers
+            = resultUsers
+            | Just maxSize' <- maxSize
+            = let resultUsers' = Set.take (fromIntegral maxSize') resultUsers
+               in if | Set.member (Right uid) resultUsers' -> resultUsers'
+                     | otherwise -> Set.insert (Right uid) $ Set.take (pred $ fromIntegral maxSize') resultUsers'
+            | otherwise = Set.singleton $ Right uid
+            where resultUsers = setOf (folded . _1) valMap
         when (maxSize > Just 1) $
           wformMessage =<< messageI Info MsgCosubmittorTip
         fmap postProcess <$> massInputW MassInput{..} submittorSettings' True (Just . Map.fromList . zip [0..] . map (, ()) $ Set.toList prefillUsers)