diff --git a/reactive.cabal b/reactive.cabal
--- a/reactive.cabal
+++ b/reactive.cabal
@@ -1,5 +1,5 @@
 Name:                reactive
-Version:             0.10.2
+Version:             0.10.3
 Synopsis:            Simple foundation for functional reactive programming
 Category:            reactivity, FRP
 Description:
diff --git a/src/FRP/Reactive/Behavior.hs b/src/FRP/Reactive/Behavior.hs
--- a/src/FRP/Reactive/Behavior.hs
+++ b/src/FRP/Reactive/Behavior.hs
@@ -143,9 +143,9 @@
 
 -- | Filter an event according to whether a reactive boolean is true.
 -- 
--- > whenE :: Event a -> Behavior Bool -> Event a
-whenE :: Ord t => EventI t a -> BehaviorI t Bool -> EventI t a
-whenE e = joinMaybes . fmap h . flip snapshot e
+-- > whenE :: Behavior Bool -> Event a -> Event a
+whenE :: Ord t => BehaviorI t Bool -> EventI t a -> EventI t a
+b `whenE` e = joinMaybes (h <$> (b `snapshot` e))
  where
    h (a,True)  = Just a
    h (_,False) = Nothing