diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,7 @@
+0.13
+----
+* Fixed an issue caused by [deserializing illegal maps](http://www.reddit.com/r/haskell/comments/1q4r3b/mindbending_behavior_for_deserialization_in/).
+
 0.11.5
 ------
 * Fixed issue #7, permitting the doctests to function against bytestring 0.9
diff --git a/bytes.cabal b/bytes.cabal
--- a/bytes.cabal
+++ b/bytes.cabal
@@ -1,6 +1,6 @@
 name:          bytes
 category:      Data, Serialization
-version:       0.12.0.1
+version:       0.13
 license:       BSD3
 cabal-version: >= 1.8
 license-file:  LICENSE
diff --git a/src/Data/Bytes/Serial.hs b/src/Data/Bytes/Serial.hs
--- a/src/Data/Bytes/Serial.hs
+++ b/src/Data/Bytes/Serial.hs
@@ -310,21 +310,21 @@
 
 instance Serial ISet.IntSet where
   serialize = serialize . ISet.toAscList
-  deserialize = ISet.fromDistinctAscList `liftM` deserialize
+  deserialize = ISet.fromList `liftM` deserialize
 
 instance Serial a => Serial (Seq.Seq a) where
   serialize = serializeWith serialize
   deserialize = deserializeWith deserialize
 
-instance Serial a => Serial (Set.Set a) where
-  serialize = serializeWith serialize
-  deserialize = deserializeWith deserialize
+instance (Serial a, Ord a) => Serial (Set.Set a) where
+  serialize = serialize . Set.toAscList
+  deserialize = Set.fromList `liftM` deserialize
 
 instance Serial v => Serial (IMap.IntMap v) where
   serialize = serializeWith serialize
   deserialize = deserializeWith deserialize
 
-instance (Serial k, Serial v) => Serial (Map.Map k v) where
+instance (Serial k, Serial v, Ord k) => Serial (Map.Map k v) where
   serialize = serializeWith serialize
   deserialize = deserializeWith deserialize
 
@@ -463,19 +463,25 @@
   serializeWith pv = serializeWith pv . F.toList
   deserializeWith gv = Seq.fromList `liftM` deserializeWith gv
 
+{-
 instance Serial1 Set.Set where
   serializeWith pv = serializeWith pv . Set.toAscList
-  deserializeWith gv = Set.fromDistinctAscList `liftM` deserializeWith gv
+  deserializeWith gv = Set.fromList `liftM` deserializeWith gv
+-}
 
 instance Serial1 IMap.IntMap where
   serializeWith pv = serializeWith (serializeWith2 serialize pv)
                    . IMap.toAscList
-  deserializeWith gv = IMap.fromDistinctAscList
+  deserializeWith gv = IMap.fromList
                `liftM` deserializeWith (deserializeWith2 deserialize gv)
 
-instance Serial k => Serial1 (Map.Map k) where
-  serializeWith = serializeWith2 serialize
-  deserializeWith = deserializeWith2 deserialize
+instance (Ord k, Serial k) => Serial1 (Map.Map k) where
+  -- serializeWith = serializeWith2 serialize
+  -- deserializeWith = deserializeWith2 deserialize
+  serializeWith pv = serializeWith (serializeWith2 serialize pv)
+                   . Map.toAscList
+  deserializeWith gv = Map.fromList
+               `liftM` deserializeWith (deserializeWith2 deserialize gv)
 
 serialize1 :: (MonadPut m, Serial1 f, Serial a) => f a -> m ()
 serialize1 = serializeWith serialize
@@ -571,8 +577,3 @@
 instance (Serial a, Serial b, Serial c) => Serial2 ((,,,,) a b c) where
   serializeWith2 f g (a, b, c, d, e) = serialize a >> serialize b >> serialize c >> f d >> g e
   deserializeWith2 m n = liftM5 (,,,,) deserialize deserialize deserialize m n
-
-instance Serial2 Map.Map where
-  serializeWith2 pk pv = serializeWith (serializeWith2 pk pv) . Map.toAscList
-  deserializeWith2 gk gv = Map.fromDistinctAscList
-                   `liftM` deserializeWith (deserializeWith2 gk gv)