diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,7 @@
+0.2.2.3
+-------
+* Added support for `safecopy` 0.9 and `cereal` 0.5
+
 0.2.2.1
 -------
 * Compiles warning-free on GHC 7.10
diff --git a/approximate.cabal b/approximate.cabal
--- a/approximate.cabal
+++ b/approximate.cabal
@@ -1,6 +1,6 @@
 name:          approximate
 category:      Numeric
-version:       0.2.2.2
+version:       0.2.2.3
 license:       BSD3
 cabal-version: >= 1.8
 license-file:  LICENSE
@@ -36,10 +36,6 @@
   default: True
   manual: True
 
-flag lib-Werror
-  default: False
-  manual: True
-
 flag herbie
   default: False
   manual: True
@@ -49,7 +45,7 @@
     base                      >= 4.3      && < 5,
     binary                    >= 0.5      && < 0.8,
     bytes                     >= 0.7      && < 1,
-    cereal                    >= 0.3.5    && < 0.5,
+    cereal                    >= 0.3.5    && < 0.6,
     comonad                   >= 3        && < 5,
     deepseq                   >= 1.3      && < 1.5,
     ghc-prim,
@@ -60,7 +56,7 @@
     pointed                   >= 3        && < 5,
     semigroupoids             >= 3.0.2    && < 6,
     semigroups                >= 0.8.4    && < 1,
-    safecopy                  >= 0.8.1    && < 0.9,
+    safecopy                  >= 0.8.1    && < 0.10,
     vector                    >= 0.9      && < 0.12
 
   if flag(herbie)
@@ -74,9 +70,6 @@
     Data.Approximate.Mass
     Data.Approximate.Numerics
 
-  if flag(lib-Werror)
-    ghc-options: -Werror
-
   if impl(ghc >= 7.4 && < 7.6)
     build-depends: ghc-prim
 
@@ -100,6 +93,3 @@
       filepath,
       semigroups     >= 0.9,
       simple-reflect >= 0.3.1
-
-  if impl(ghc<7.6.1) && flag(lib-Werror)
-    ghc-options: -Werror
diff --git a/src/Data/Approximate/Mass.hs b/src/Data/Approximate/Mass.hs
--- a/src/Data/Approximate/Mass.hs
+++ b/src/Data/Approximate/Mass.hs
@@ -189,7 +189,7 @@
   {-# INLINE (>>-) #-}
 
 instance Monad Mass where
-  return = Mass 1
+  return = pure
   {-# INLINE return #-}
   Mass p a >>= f = case f a of
     Mass q b -> Mass (p * q) b