diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 0.4.17
+
+* Case insensitive proxy environment variables [#135](https://github.com/snoyberg/http-client/issues/135)
+
 ## 0.4.16
 
 * Proxy auth for HTTPS [#132](https://github.com/snoyberg/http-client/issues/132)
diff --git a/Network/HTTP/Client/Manager.hs b/Network/HTTP/Client/Manager.hs
--- a/Network/HTTP/Client/Manager.hs
+++ b/Network/HTTP/Client/Manager.hs
@@ -25,6 +25,8 @@
 #if !MIN_VERSION_base(4,6,0)
 import Prelude hiding (catch)
 #endif
+import Control.Applicative ((<|>))
+import Control.Arrow (first)
 import Data.Monoid (mappend)
 import System.IO (hClose, hFlush, IOMode(..))
 import qualified Data.IORef as I
@@ -502,7 +504,8 @@
 envHelper :: Text -> EnvHelper -> IO (Request -> Request)
 envHelper name eh = do
     env <- getEnvironment
-    case lookup (T.unpack name) env of
+    let lenv = Map.fromList $ map (first $ T.toLower . T.pack) env
+    case lookup (T.unpack name) env <|> Map.lookup name lenv of
         Nothing  -> return noEnvProxy
         Just ""  -> return noEnvProxy
         Just str -> do
diff --git a/http-client.cabal b/http-client.cabal
--- a/http-client.cabal
+++ b/http-client.cabal
@@ -1,5 +1,5 @@
 name:                http-client
-version:             0.4.16
+version:             0.4.17
 synopsis:            An HTTP client engine, intended as a base layer for more user-friendly packages.
 description:         Hackage documentation generation is not reliable. For up to date documentation, please see: <http://www.stackage.org/package/http-client>.
 homepage:            https://github.com/snoyberg/http-client