diff --git a/rhine/src/FRP/Rhine/ClSF/Util.hs b/rhine/src/FRP/Rhine/ClSF/Util.hs
index fe28061c1..9c0ec1ffd 100644
--- a/rhine/src/FRP/Rhine/ClSF/Util.hs
+++ b/rhine/src/FRP/Rhine/ClSF/Util.hs
@@ -16,7 +16,8 @@ module FRP.Rhine.ClSF.Util where
 import Control.Arrow
 import Control.Category (Category)
 import qualified Control.Category (id)
-import Data.Maybe (fromJust)
+import Data.Functor (($>))
+import Data.Maybe (fromMaybe)
 import Data.Monoid (Last (Last), getLast)
 
 -- containers
@@ -26,7 +27,7 @@ import Data.Sequence
 import Control.Monad.Trans.Reader (ask, asks)
 
 -- dunai
-import Control.Monad.Trans.MSF.Reader (readerS)
+import Control.Monad.Trans.MSF.Reader (readerS, runReaderS)
 import Data.MonadicStreamFunction.Instances.Num ()
 import Data.MonadicStreamFunction.Instances.VectorSpace ()
 
@@ -436,10 +437,20 @@ scaledTimer ::
   BehaviorF (ExceptT () m) td a (Diff td)
 scaledTimer diff = timer diff >>> arr (/ diff)
 
+-- * Ad-hoc re-clocking utilities
+
+-- | Define a local clock for one 'BehaviourF' which ticks exactly when the input is @'Just' a@.
+onLocalClock :: (Monad m, TimeDomain td) => BehaviourF m td a b -> BehaviourF m td (Maybe a) (Maybe b)
+onLocalClock behaviour = readerS $ proc (ti, aMaybe) -> do
+  let now = absolute ti
+  x <- iPre mempty <<< mappendS -< Last $ aMaybe $> now
+  let sinceLast' = maybe (sinceLast ti) (`diffTime` now) $ getLast x
+  mapMaybeS $ runReaderS behaviour -< (ti {sinceLast = sinceLast'},) <$> aMaybe
+
 -- * To be ported to Dunai
 
 {- | Remembers the last 'Just' value,
    defaulting to the given initialisation value.
 -}
 lastS :: (Monad m) => a -> MSF m (Maybe a) a
-lastS a = arr Last >>> mappendFrom (Last (Just a)) >>> arr (getLast >>> fromJust)
+lastS a = arr Last >>> mappendS >>> arr (getLast >>> fromMaybe a)