diff --git a/src/Handler/Course/ParticipantInvite.hs b/src/Handler/Course/ParticipantInvite.hs
index 4bdf04021..14cd08930 100644
--- a/src/Handler/Course/ParticipantInvite.hs
+++ b/src/Handler/Course/ParticipantInvite.hs
@@ -49,11 +49,19 @@ tutorialTemplateNames Nothing     = ["Vorlage", "Template"]
 tutorialTemplateNames (Just name) = [prefixes <> suffixes | prefixes <- tutorialTemplateNames Nothing, suffixes <- [mempty, tutorialTypeSeparator <> name]]
 
 tutorialDefaultName :: Maybe TutorialType -> Day -> TutorialName
-tutorialDefaultName Nothing     = string2citext . formatTime defaultTimeLocale "%y_%m_%d" -- Don't use user date display setting, so that tutorial default names conform to all users
+tutorialDefaultName Nothing     = formatDayForTutName 
 tutorialDefaultName (Just ttyp) = 
   let prefix = CI.mk $ snd $ Text.breakOnEnd (CI.original tutorialTypeSeparator) $ CI.original ttyp
   in  (<> (tutorialTypeSeparator <> prefix)) . tutorialDefaultName Nothing
 
+formatDayForTutName :: Day -> CI Text -- "%yy_%mm_%dd" -- Do not use user date display setting, since tutorial default names must be universal regardless of user
+-- formatDayForTutName = CI.mk . formatTime' "%y_%m_%d" -- we don't want to go monadic for this
+formatDayForTutName d = CI.mk . Text.map d2u . Text.drop 2 . tshow 
+  where 
+    d2u '-' = '_'
+    d2u  c  =  c
+
+
 data ButtonCourseRegisterMode = BtnCourseRegisterConfirm | BtnCourseRegisterAbort
   deriving (Eq, Ord, Enum, Bounded, Read, Show, Generic)
 instance Universe ButtonCourseRegisterMode