diff --git a/Data/FingerTree/PSQueue.hs b/Data/FingerTree/PSQueue.hs
--- a/Data/FingerTree/PSQueue.hs
+++ b/Data/FingerTree/PSQueue.hs
@@ -16,7 +16,8 @@
                         Measured (..), split, viewl, (><))
 import Data.Monoid
 import Data.Ord
-import Data.List
+import Data.List hiding (lookup)
+import Prelude hiding (lookup)
 
 data Prio k a = Prio (Binding k a) | PMax
   deriving (Eq, Ord, Show)
@@ -35,8 +36,8 @@
         mappend x NoKey = x
         mappend x y     = y
 
-geqKey k NoKey = False
-geqKey k (Key k') = k >= k'
+leqKey k NoKey = False
+leqKey k (Key k') = k <= k'
 
 data Binding k p = k :-> p
   deriving (Eq, Ord, Show)
@@ -93,7 +94,7 @@
 -- or update a priority in a queue.
 alter :: (Ord k, Ord p) => (Maybe p -> Maybe p) -> k -> PSQ k p -> PSQ k p
 alter f k (PSQ q) =
-  PSQ $ let (u,v) = split (geqKey k . kpsKey) q
+  PSQ $ let (u,v) = split (leqKey k . kpsKey) q
          in case viewl v of
               EmptyL -> case f Nothing of
                            Nothing -> q
@@ -101,7 +102,7 @@
               (k' :-> p') :< v'
                 | k == k'   -> case f (Just p') of
                                  Nothing -> u >< v'
-                                 Just p  -> u >< ((k :-> p') <| v')
+                                 Just p  -> u >< ((k :-> p) <| v')
                 | otherwise -> case f Nothing of
                                  Nothing -> u >< v
                                  Just p  -> u >< ((k :-> p) <| v)
diff --git a/fingertree-psqueue.cabal b/fingertree-psqueue.cabal
--- a/fingertree-psqueue.cabal
+++ b/fingertree-psqueue.cabal
@@ -1,5 +1,5 @@
 name:                fingertree-psqueue
-version:             0.1
+version:             0.2
 cabal-version:       >= 1.2
 build-type:          Simple