diff --git a/src/GB/CPU.hs b/src/GB/CPU.hs
index fdbf17e..9d5b4ba 100644
--- a/src/GB/CPU.hs
+++ b/src/GB/CPU.hs
@@ -128,13 +128,13 @@ execute cpu = \case
   IncHL -> let target = getHL $ cpu ^. registers
                value = fetch cpu target
                (newValue, newFlags) = add value 1 False in
-           cpu & bus %~ (flip V.update $ V.singleton (fromIntegral target, newValue)) & registers . flags .~ newFlags
+           write cpu target newValue & registers . flags .~ newFlags
   DecR t -> let (value, newFlags) = sub (cpu ^. registers . t) 1 False in
             cpu & registers . t .~ value & registers . flags .~ newFlags
   DecHL -> let target = getHL $ cpu ^. registers
                value = fetch cpu target
                (newValue, newFlags) = sub value 1 False in
-           cpu & bus %~ (flip V.update $ V.singleton (fromIntegral target, newValue)) & registers . flags .~ newFlags
+           write cpu target newValue & registers . flags .~ newFlags
   where
     add :: Word8 -> Word8 -> Bool -> (Word8, FlagRegister)
     add o n _c = let new        = o + n + if _c then 1 else 0
@@ -143,8 +143,6 @@ execute cpu = \case
                      _carry     = o > new
                      _halfCarry = o .&. 16 + n .&. 16 > 16 in
                  (new, FlagRegister {..})
-    fetch :: CPU -> Word16 -> Word8
-    fetch _cpu addr = flip V.index (fromIntegral addr) $ _cpu ^. bus
 
     sub :: Word8 -> Word8 -> Bool -> (Word8, FlagRegister)
     sub o n _c = let new        = o - n - if _c then 1 else 0
@@ -153,3 +151,9 @@ execute cpu = \case
                      _carry     = o > new
                      _halfCarry = o .&. 16 + n .&. 16 > 16 in
                  (new, FlagRegister {..})
+
+    fetch :: CPU -> Word16 -> Word8
+    fetch _cpu addr = flip V.index (fromIntegral addr) $ _cpu ^. bus
+
+    write :: CPU -> Word16 -> Word8 -> CPU
+    write _cpu target value = _cpu & bus %~ (flip V.update $ V.singleton (fromIntegral target, value))