diff --git a/Data/Memory/PtrMethods.hs b/Data/Memory/PtrMethods.hs
--- a/Data/Memory/PtrMethods.hs
+++ b/Data/Memory/PtrMethods.hs
@@ -54,7 +54,7 @@
   where
     loop _   _  0 = return ()
     loop !d !s !n = do
-        peek s >>= poke s . xor v
+        peek s >>= poke d . xor v
         loop (d `plusPtr` 1) (s `plusPtr` 1) (n-1)
 
     loopInplace _   0 = return ()
diff --git a/memory.cabal b/memory.cabal
--- a/memory.cabal
+++ b/memory.cabal
@@ -1,5 +1,5 @@
 Name:                memory
-Version:             0.14.4
+Version:             0.14.5
 Synopsis:            memory and related abstraction stuff
 Description:
     Chunk of memory, polymorphic byte array management and manipulation