diff --git a/src/Handler/Exam/Users.hs b/src/Handler/Exam/Users.hs
index 1912abbd0..9fcf76c04 100644
--- a/src/Handler/Exam/Users.hs
+++ b/src/Handler/Exam/Users.hs
@@ -973,7 +973,7 @@ postEUsersR tid ssh csh examn = do
 
               guessUser' :: ExamUserTableCsv -> DB (Bool, UserId)
               guessUser' ExamUserTableCsv{..} = do
-                let criteria = PredDNF $ Set.singleton $ impureNonNull $ Set.fromList $ (PLVariable <$>) $ catMaybes
+                let criteria = PredDNF . maybe Set.empty Set.singleton . fromNullable . Set.fromList . fmap PLVariable $ catMaybes
                       [ GuessUserMatrikelnummer <$> csvEUserMatriculation
                       , GuessUserDisplayName <$> csvEUserName
                       , GuessUserSurname <$> csvEUserSurname