diff --git a/cabal-install/Distribution/Client/Sandbox.hs b/cabal-install/Distribution/Client/Sandbox.hs
index 561d6f833e4df29e0bafd0d41170200bd67c7f05..8b6c239e57f8c7754f7299007773c4affeb1eecd 100644
--- a/cabal-install/Distribution/Client/Sandbox.hs
+++ b/cabal-install/Distribution/Client/Sandbox.hs
@@ -169,8 +169,7 @@ updateSandboxConfigFileFlag globalFlags =
   case globalSandboxConfigFile globalFlags of
     Flag _ -> return globalFlags
     NoFlag -> do
-      f' <- fmap (fromMaybe NoFlag . fmap Flag) . lookupEnv
-            $ "CABAL_SANDBOX_CONFIG"
+      f' <- fmap (maybe NoFlag Flag) . lookupEnv $ "CABAL_SANDBOX_CONFIG"
       return globalFlags { globalSandboxConfigFile = f' }
 
 -- | Return the path to the sandbox config file - either the default or the one