diff --git a/dequeue.cabal b/dequeue.cabal
--- a/dequeue.cabal
+++ b/dequeue.cabal
@@ -1,7 +1,7 @@
 Build-Type: Simple
 Name: dequeue
 Category: Data Structures
-Version: 0.1.5
+Version: 0.1.7
 Cabal-Version: >= 1.2
 Synopsis: A typeclass and an implementation for double-ended queues.
 Description:
@@ -17,7 +17,7 @@
 
 Library
     Exposed-Modules: Data.Dequeue, Data.Dequeue.Show
-    Build-Depends: base < 5, safe, QuickCheck
+    Build-Depends: base < 5, safe, QuickCheck >= 2
     Hs-Source-Dirs: src
     GHC-Options: -Wall
 
diff --git a/src/Data/Dequeue.hs b/src/Data/Dequeue.hs
--- a/src/Data/Dequeue.hs
+++ b/src/Data/Dequeue.hs
@@ -62,13 +62,11 @@
 import qualified Data.Dequeue.Show
 
 -- | A typeclass for double-ended queues.
-class Dequeue q where
+class Foldable q => Dequeue q where
     -- | Generates an empty queue.
     empty :: q a
     -- | Returns 'True' if this queue is empty.
     null :: q a -> Bool
-    -- | Returns the number of elements in this queue.
-    length :: q a -> Int
     -- | Returns the item on the front of the queue.
     first :: q a -> Maybe a
     -- | Returns the item on the end of the queue.
@@ -82,11 +80,11 @@
     -- | Pushes an item onto the front of the queue.
     pushFront :: q a -> a -> q a
     -- | Pops an item from the front of the queue.
-    popFront :: q a -> (Maybe a, q a)
+    popFront :: q a -> Maybe (a, q a)
     -- | Pushes an item onto the back of the queue.
     pushBack :: q a -> a -> q a
     -- | Pops an item from the back of the queue.
-    popBack :: q a -> (Maybe a, q a)
+    popBack :: q a -> Maybe (a, q a)
     -- | Converts a list into a queue.
     fromList :: [a] -> q a
 
@@ -125,15 +123,15 @@
 --   you get the same queue.
 prop_pushpop_front :: (Dequeue q, Eq a, Eq (q a)) => q a -> a -> Bool
 prop_pushpop_front q a =
-    let (a', q') = popFront (pushFront q a) in
-    a' == Just a && q' == q
+    let Just (a', q') = popFront (pushFront q a) in
+    a' == a && q' == q
 
 -- | Validates that if you push, then pop, the back of the queue,
 --   you get the same queue.
 prop_pushpop_back :: (Dequeue q, Eq a, Eq (q a)) => q a -> a -> Bool
 prop_pushpop_back q a =
-    let (a', q') = popBack (pushBack q a) in
-    a' == Just a && q' == q
+    let Just (a', q') = popBack (pushBack q a) in
+    a' == a && q' == q
 
 -- | Validates that 'first' returns the last 'pushFront''d element.
 prop_push_front :: (Dequeue q, Eq a) => q a -> a -> Bool
@@ -199,12 +197,12 @@
     foldl f a (BankersDequeue _ front _ rear) = foldl f a (front ++ reverse rear)
     foldr1 f (BankersDequeue _ front _ rear) = foldr1 f (front ++ reverse rear)
     foldl1 f (BankersDequeue _ front _ rear) = foldl1 f (front ++ reverse rear)
+    length (BankersDequeue sizeF _ sizeR _) = sizeF + sizeR
 
 instance Dequeue BankersDequeue where
     empty = BankersDequeue 0 [] 0 []
     null (BankersDequeue 0 [] 0 []) = True
     null _ = False
-    length (BankersDequeue sizeF _ sizeR _) = sizeF + sizeR
     first (BankersDequeue _ [] _ [x]) = Just x
     first (BankersDequeue _ front _ _) =  headMay front
     last (BankersDequeue _ [x] _ []) = Just x
@@ -215,18 +213,18 @@
         take i rear ++ take (i - sizeR) (reverse front)
     pushFront (BankersDequeue sizeF front sizeR rear) x =
         check $ BankersDequeue (sizeF + 1) (x : front) sizeR rear
-    popFront (BankersDequeue _ [] _ []) = (Nothing, empty)
-    popFront (BankersDequeue _ [] _ [x]) = (Just x, empty)
+    popFront (BankersDequeue _ [] _ []) = Nothing
+    popFront (BankersDequeue _ [] _ [x]) = Just (x, empty)
     popFront (BankersDequeue _ [] _ _) = error "Queue is too far unbalanced."
     popFront (BankersDequeue sizeF (f : fs) sizeR rear) =
-        (Just f, check $ BankersDequeue (sizeF - 1) fs sizeR rear)
+        Just (f, check $ BankersDequeue (sizeF - 1) fs sizeR rear)
     pushBack (BankersDequeue sizeF front sizeR rear) x =
         check $ BankersDequeue sizeF front (sizeR + 1) (x : rear)
-    popBack (BankersDequeue _ [] _ []) = (Nothing, empty)
-    popBack (BankersDequeue _ [x] _ []) = (Just x, empty)
+    popBack (BankersDequeue _ [] _ []) = Nothing
+    popBack (BankersDequeue _ [x] _ []) = Just (x, empty)
     popBack (BankersDequeue _ _ _ []) = error "Queue is too far unbalanced."
     popBack (BankersDequeue sizeF front sizeR (r : rs)) =
-        (Just r, check $ BankersDequeue sizeF front (sizeR - 1) rs)
+        Just (r, check $ BankersDequeue sizeF front (sizeR - 1) rs)
     fromList list = check $ BankersDequeue (List.length list) list 0 []
 
 -- | The maximum number of times longer one half of a 'BankersDequeue' is
@@ -336,7 +334,7 @@
 --   pops from the front.
 prop_pop_front_bq_balance :: BankersDequeue Int -> Int -> Bool
 prop_pop_front_bq_balance q count =
-    let pop _ queue = let (_, queue') = popFront queue in queue'
+    let pop _ queue = (fromJustDef queue . liftM snd . popFront) queue
         q' = foldr pop q [0 .. count] in
     balanced q'
 
@@ -344,7 +342,7 @@
 --   pops from the back.
 prop_pop_back_bq_balance :: BankersDequeue Int -> Int -> Bool
 prop_pop_back_bq_balance q count =
-    let pop _ queue = let (_, queue') = popBack queue in queue'
+    let pop _ queue = (fromJustDef queue . liftM snd . popBack) queue
         q' = foldr pop q [0 .. count] in
     balanced q'