diff --git a/Data/Aeson/Types/Instances.hs b/Data/Aeson/Types/Instances.hs
--- a/Data/Aeson/Types/Instances.hs
+++ b/Data/Aeson/Types/Instances.hs
@@ -78,11 +78,6 @@
 import Data.Vector (Vector)
 import Data.Word (Word, Word8, Word16, Word32, Word64)
 import Foreign.Storable (Storable)
-#if MIN_VERSION_time(1,5,0)
-import Data.Time.Format(defaultTimeLocale, dateTimeFmt)
-#else
-import System.Locale (defaultTimeLocale, dateTimeFmt)
-#endif
 import qualified Data.HashMap.Strict as H
 import qualified Data.HashSet as HashSet
 import qualified Data.IntMap as IntMap
@@ -99,6 +94,12 @@
 import qualified Data.Vector.Storable as VS
 import qualified Data.Vector.Unboxed as VU
 import qualified Data.Vector.Mutable as VM ( unsafeNew, unsafeWrite )
+
+#if MIN_VERSION_time(1,5,0)
+import Data.Time.Format (defaultTimeLocale, dateTimeFmt)
+#else
+import System.Locale (defaultTimeLocale, dateTimeFmt)
+#endif
 
 instance (ToJSON a) => ToJSON (Identity a) where
     toJSON (Identity a) = toJSON a
diff --git a/aeson.cabal b/aeson.cabal
--- a/aeson.cabal
+++ b/aeson.cabal
@@ -1,5 +1,5 @@
 name:            aeson
-version:         0.8.1.0
+version:         0.8.1.1
 license:         BSD3
 license-file:    LICENSE
 category:        Text, Web, JSON
@@ -113,7 +113,7 @@
     template-haskell >= 2.4,
     text >= 1.1.1.0,
     transformers,
-    unordered-containers >= 0.2.3.0,
+    unordered-containers >= 0.2.5.0,
     vector >= 0.7.1
 
   if flag(old-locale)
@@ -122,6 +122,7 @@
     build-depends: time >= 1.5
 
   if flag(developer)
+    ghc-options: -Werror
     ghc-prof-options: -auto-all
 
   ghc-options: -O2 -Wall
@@ -151,7 +152,6 @@
     bytestring,
     containers,
     ghc-prim >= 0.2,
-    old-locale,
     template-haskell,
     test-framework,
     test-framework-hunit,
@@ -160,6 +160,11 @@
     time,
     unordered-containers,
     vector
+
+  if flag(old-locale)
+    build-depends: time < 1.5, old-locale
+  else
+    build-depends: time >= 1.5
 
 source-repository head
   type:     git
diff --git a/tests/Properties.hs b/tests/Properties.hs
--- a/tests/Properties.hs
+++ b/tests/Properties.hs
@@ -23,14 +23,18 @@
 import Types
 import Encoders
 import Properties.Deprecated (deprecatedTests)
+import System.IO
+import System.IO.Unsafe (unsafePerformIO)
+
 #ifdef GHC_GENERICS
 import Data.Int
 import qualified Data.Map as Map
 #endif
 
-import System.IO
-import System.IO.Unsafe (unsafePerformIO)
-import System.Locale
+#if !MIN_VERSION_time(1,5,0)
+import System.Locale (defaultTimeLocale, dateTimeFmt)
+#endif
+
 
 roundTripCamel :: String -> Assertion
 roundTripCamel name = assertEqual "" name (camelFrom '_' $ camelTo '_' name)