diff --git a/src/Actions.hs b/src/Actions.hs
index 3fcf04a8d..3d1660711 100644
--- a/src/Actions.hs
+++ b/src/Actions.hs
@@ -490,9 +490,11 @@ search =
   do
     Level   { lmap = lmap } <- gets slevel
     Movable { mloc = ploc } <- gets splayer
-    let searchTile (Tile (Door hv (Just n)) x,t') = Just (Tile (Door hv (Just (max (n - 1) 0))) x, t')
-        searchTile t                              = Just t
-        slmap = foldl (\ l m -> update searchTile (shift ploc m) l) lmap moves
+    let searchTile (Tile (Door hv (Just n)) x, t') =
+          (Tile (Door hv (Just (max (n - 1) 0))) x, t')
+        searchTile t = t
+        f l m = M.adjust searchTile (shift ploc m) l
+        slmap = foldl' f lmap moves
     modify (updateLevel (updateLMap (const slmap)))
 
 -- | Start the floor targeting mode or toggle between the two floor modes.
diff --git a/src/Item.hs b/src/Item.hs
index 63cbff8fb..aef275e51 100644
--- a/src/Item.hs
+++ b/src/Item.hs
@@ -245,7 +245,7 @@ strongestSword :: [Item] -> Int
 strongestSword l =
   let aux acc (Item { itype = Sword i }) = max acc i
       aux acc _ = acc
-  in  foldl aux 0 l
+  in  foldl' aux 0 l
 
 makeObject :: Int -> (String -> String) -> String -> String
 makeObject 1 adj obj = let b = adj obj
diff --git a/src/LambdaHack.hs b/src/LambdaHack.hs
index 0dcbaeb1b..d31ca53cc 100644
--- a/src/LambdaHack.hs
+++ b/src/LambdaHack.hs
@@ -2,6 +2,7 @@ module Main where
 
 import System.Directory
 import Control.Monad
+import Data.List as L
 import Data.Map as M
 
 import Action
@@ -79,5 +80,5 @@ generate config session msg =
          defState = defaultState player dng lvl
          state = defState { sassocs = assocs, sconfig = config }
          k = Config.get config "heroes" "extraHeroes"
-         hstate = foldl (addHero hp) state [1..k]
+         hstate = foldl' (addHero hp) state [1..k]
      handlerToIO session hstate msg handle
diff --git a/src/Level.hs b/src/Level.hs
index c48025abc..044f35acb 100644
--- a/src/Level.hs
+++ b/src/Level.hs
@@ -559,7 +559,7 @@ viewSmell n = let k | n > 9    = '*'
 --       Scatter randomly or not?
 scatterItems :: [Item] -> Loc -> Level -> Level
 scatterItems items loc lvl@(Level { lmap = lmap }) =
-  let joinItems items = foldl (\ acc i -> snd (joinItem i acc)) items
+  let joinItems items = foldl' (\ acc i -> snd (joinItem i acc)) items
       t = lmap `at` loc
       nt = t { titems = joinItems items (titems t) }
       ntRemember = lmap `rememberAt` loc