diff --git a/src/Handler/Utils/Submission.hs b/src/Handler/Utils/Submission.hs
index ee7e7fc56..c6bce6821 100644
--- a/src/Handler/Utils/Submission.hs
+++ b/src/Handler/Utils/Submission.hs
@@ -678,12 +678,13 @@ sinkMultiSubmission userId isUpdate = do
         acc (Just sId, fp) segment = return (Just sId, fp ++ [segment])
         acc (Nothing , fp) segment = do
           let
-            tryDecrypt (Text.pack -> ciphertext)
+            segments' = filter (not . Text.null) . Text.split (flip Set.notMember cryptoIdChars . CI.mk) $ Text.pack segment
+            tryDecrypt ciphertext
               | Just cID <- fromPathPiece ciphertext = do
                   sId <- decrypt (cID :: CryptoFileNameSubmission)
                   Just sId <$ get404 sId
               | otherwise = return Nothing
-          msId <- lift (lift (tryDecrypt segment) `catches` [ E.Handler handleCryptoID, E.Handler (handleHCError $ Right fileTitle) ])
+          Alt msId <- lift . flip foldMapM segments' $ \seg -> Alt <$> lift (tryDecrypt seg) `catches` [ E.Handler handleCryptoID, E.Handler (handleHCError $ Right fileTitle) ]
           return (msId, fp)
       (msId, (joinPath -> fileTitle')) <- foldM acc (Nothing, []) $ splitDirectories fileTitle
       case msId of
@@ -708,6 +709,9 @@ sinkMultiSubmission userId isUpdate = do
     handleCryptoID :: CryptoIDError -> _ (Maybe a)
     handleCryptoID _ = return Nothing
 
+    cryptoIdChars :: Set (CI Char)
+    cryptoIdChars = Set.fromList . map CI.mk $ "uwa" ++ "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
+
 
 submissionMatchesSheet :: TermId -> SchoolId -> CourseShorthand -> SheetName -> CryptoFileNameSubmission -> DB SubmissionId
 submissionMatchesSheet tid ssh csh shn cid = do