diff --git a/src/Dodge/Projectile/Update.hs b/src/Dodge/Projectile/Update.hs
index f1fc08dcb..6c69bc070 100644
--- a/src/Dodge/Projectile/Update.hs
+++ b/src/Dodge/Projectile/Update.hs
@@ -204,25 +204,23 @@ pjRemoteSetDirection ph pj w = case ph of
     pjlens = cWorld . lWorld . projectiles . ix (pj ^. pjID)
 
 moveStuckGrenade :: Int -> Point3 -> Float -> Projectile -> World -> World
-moveStuckGrenade cid poff d pj w
-    | Just cr <- w ^? cWorld . lWorld . creatures . ix cid =
-        let cpos = cr ^. crPos
-            cdir = cr ^. crDir
-            vel = cpos - cr ^. crOldPos
-         in w
-                & pjlens . pjPos . _xy .~ xyV3 (cpos + rotate3z cdir poff)
-                & pjlens . pjDir .~ d + cdir
-                & pjlens . pjVel .~ vel
-    | otherwise =
-        w & pjlens . pjType .~ Grenade GStick
+moveStuckGrenade cid poff d pj w = fromMaybe (w & pjlens . pjType .~ Grenade GStick) $ do
+    cr <- w ^? cWorld . lWorld . creatures . ix cid
+    let cpos = cr ^. crPos
+        cdir = cr ^. crDir
+    return $
+        w
+            & pjlens . pjPos . _xy .~ xyV3 (cpos + rotate3z cdir poff)
+            & pjlens . pjDir .~ d + cdir
+            & pjlens . pjVel .~ (cpos - cr ^. crOldPos)
   where
     pjlens = cWorld . lWorld . projectiles . ix (pj ^. pjID)
 
 moveProjectile :: Projectile -> World -> World
 moveProjectile pj w
     | Just GStuckWall{} <- pj ^? pjType . gnHitEffect = w
-    | Just (GStuckCreature crid poff d) <- pj ^? pjType . gnHitEffect =
-        moveStuckGrenade crid poff d pj w
+    | Just (GStuckCreature cid poff d) <- pj ^? pjType . gnHitEffect =
+        moveStuckGrenade cid poff d pj w
     | otherwise = case collide3 sp (sp + _pjVel pj) w of
         (p, Just (n, OWall wl)) -> shellHitWall p n wl pj w
         (p, Just (_, OFloor)) -> shellHitFloor p pj w
diff --git a/src/Geometry/Polygon.hs b/src/Geometry/Polygon.hs
index dfcaa8715..47350a949 100644
--- a/src/Geometry/Polygon.hs
+++ b/src/Geometry/Polygon.hs
@@ -9,6 +9,7 @@ import Geometry.Data
 import Geometry.LHS
 import Geometry.Vector
 import ListHelp
+import Linear
 
 -- | Draw an anticlockwise rectangle based on maximal N S W E values.
 rectNSWE :: Float -> Float -> Float -> Float -> [Point2]
@@ -153,7 +154,7 @@ convexHullSafe _ = []
 grahamScan :: [Point2] -> [Point2]
 grahamScan = foldr push []
   where
-    push point stack = grahamEliminate (point : stack)
+    push p stack = grahamEliminate (p : stack)
 
 {- | Remove second element if top three elements are not counterclockwise.
  Repeat if necessary. See
@@ -164,8 +165,8 @@ grahamEliminate (x : y : z : xs)
     | not $ isLHS x y z = grahamEliminate (x : z : xs)
 grahamEliminate xs = xs
 
-centroid :: Foldable t => t Point2 -> Point2
-centroid = L.fold $ (/) <$> L.Fold (+.+) (V2 0 0) id <*> L.genericLength
+centroid :: (Num (f a),Functor f, Fractional a,Foldable t) => t (f a) -> f a
+centroid = L.fold $ (^/) <$> L.Fold (+) 0 id <*> L.genericLength
 
 centroidNum :: (Fractional a, Foldable t) => t a -> a
 centroidNum = L.fold $ (/) <$> L.Fold (+) 0 id <*> L.genericLength