diff --git a/XMonad/Actions/GridSelect.hs b/XMonad/Actions/GridSelect.hs
index f33f0dcd..1ba0aa63 100644
--- a/XMonad/Actions/GridSelect.hs
+++ b/XMonad/Actions/GridSelect.hs
@@ -409,7 +409,7 @@ makeXEventhandler keyhandler = fix $ \me -> join $ liftX $ withDisplay $ \d -> l
                                then do
                                   (ks,s) <- lookupString $ asKeyEvent e
                                   return $ do
-                                      mask <- liftX $ cleanMask (ev_state ev)
+                                      mask <- liftX $ cleanKeyMask <*> pure (ev_state ev)
                                       keyhandler (fromMaybe xK_VoidSymbol ks, s, mask)
                                else
                                   return $ stdHandle ev me
diff --git a/XMonad/Actions/TreeSelect.hs b/XMonad/Actions/TreeSelect.hs
index 110930a7..8727634e 100644
--- a/XMonad/Actions/TreeSelect.hs
+++ b/XMonad/Actions/TreeSelect.hs
@@ -535,7 +535,7 @@ navigate = gets tss_display >>= \d -> join . liftIO . allocaXEvent $ \e -> do
     if | ev_event_type ev == keyPress -> do
            (ks, _) <- lookupString $ asKeyEvent e
            return $ do
-               mask <- liftX $ cleanMask (ev_state ev)
+               mask <- liftX $ cleanKeyMask <*> pure (ev_state ev)
                f <- asks ts_navigate
                fromMaybe navigate $ M.lookup (mask, fromMaybe xK_VoidSymbol ks) f
        | ev_event_type ev == buttonPress -> do
diff --git a/XMonad/Prelude.hs b/XMonad/Prelude.hs
index de2a83cf..227211d1 100644
--- a/XMonad/Prelude.hs
+++ b/XMonad/Prelude.hs
@@ -24,6 +24,7 @@ module XMonad.Prelude (
     safeGetWindowAttributes,
     keyToString,
     keymaskToString,
+    cleanKeyMask,
 ) where
 
 import Foreign (alloca, peek)
@@ -116,3 +117,18 @@ keymaskToString numLockMask msk =
 -- pair, into a string.
 keyToString :: (KeyMask, KeySym) -> [Char]
 keyToString = uncurry (++) . bimap (keymaskToString 0) keysymToString
+
+-- | Strip numlock, capslock, mouse buttons and XKB group from a 'KeyMask',
+-- leaving only modifier keys like Shift, Control, Super, Hyper in the mask
+-- (hence the \"Key\" in \"cleanKeyMask\").
+--
+-- Core's 'cleanMask' only strips the first two because key events from
+-- passive grabs (key bindings) are stripped of mouse buttons and XKB group by
+-- the X server already for compatibility reasons. For more info, see:
+-- <https://www.x.org/releases/X11R7.7/doc/kbproto/xkbproto.html#Delivering_a_Key_or_Button_Event_to_a_Client>
+cleanKeyMask :: X (KeyMask -> KeyMask)
+cleanKeyMask = cleanKeyMask' <$> gets numberlockMask
+
+cleanKeyMask' :: KeyMask -> KeyMask -> KeyMask
+cleanKeyMask' numLockMask mask =
+    mask .&. complement (numLockMask .|. lockMask) .&. (button1Mask - 1)