diff --git a/Cabal/src/Distribution/GetOpt.hs b/Cabal/src/Distribution/GetOpt.hs
index a55599496c6..e77c8fd7c55 100644
--- a/Cabal/src/Distribution/GetOpt.hs
+++ b/Cabal/src/Distribution/GetOpt.hs
@@ -63,12 +63,12 @@ data ArgDescr a
   | -- |   option requires argument
     ReqArg (String -> Either String a) String
   | -- |   optional argument
-    OptArg String (Maybe String -> Either String a) String
+    OptArg (Maybe String -> Either String a) String
 
 instance Functor ArgDescr where
   fmap f (NoArg a) = NoArg (f a)
   fmap f (ReqArg g s) = ReqArg (fmap f . g) s
-  fmap f (OptArg dv g s) = OptArg dv (fmap f . g) s
+  fmap f (OptArg g s) = OptArg (fmap f . g) s
 
 data OptKind a -- kind of cmd line arg (internal use only):
   = Opt a --    an option
@@ -140,7 +140,7 @@ fmtShort (NoArg _) so = "-" ++ [so]
 fmtShort (ReqArg _ ad) so =
   let opt = "-" ++ [so]
    in opt ++ " " ++ ad ++ " or " ++ opt ++ ad
-fmtShort (OptArg _ _ ad) so =
+fmtShort (OptArg _ ad) so =
   let opt = "-" ++ [so]
    in opt ++ "[" ++ ad ++ "]"
 
@@ -158,7 +158,7 @@ fmtLong (NoArg _) lo = "--" ++ lo
 fmtLong (ReqArg _ ad) lo =
   let opt = "--" ++ lo
    in opt ++ "=" ++ ad
-fmtLong (OptArg _ _ ad) lo =
+fmtLong (OptArg _ ad) lo =
   let opt = "--" ++ lo
    in opt ++ "[=" ++ ad ++ "]"
 
@@ -250,8 +250,8 @@ longOpt ls rs optDescr = long ads arg rs
     long [ReqArg _ d] [] [] = (errReq d optStr, [])
     long [ReqArg f _] [] (r : rest) = (fromRes (f r), rest)
     long [ReqArg f _] ('=' : xs) rest = (fromRes (f xs), rest)
-    long [OptArg _ f _] [] rest = (fromRes (f Nothing), rest)
-    long [OptArg _ f _] ('=' : xs) rest = (fromRes (f (Just xs)), rest)
+    long [OptArg f _] [] rest = (fromRes (f Nothing), rest)
+    long [OptArg f _] ('=' : xs) rest = (fromRes (f (Just xs)), rest)
     long _ _ rest = (UnreqOpt ("--" ++ ls), rest)
 
 -- handle short option
@@ -269,8 +269,8 @@ shortOpt y ys rs optDescr = short ads ys rs
     short (ReqArg _ d : _) [] [] = (errReq d optStr, [])
     short (ReqArg f _ : _) [] (r : rest) = (fromRes (f r), rest)
     short (ReqArg f _ : _) xs rest = (fromRes (f xs), rest)
-    short (OptArg _ f _ : _) [] rest = (fromRes (f Nothing), rest)
-    short (OptArg _ f _ : _) xs rest = (fromRes (f (Just xs)), rest)
+    short (OptArg f _ : _) [] rest = (fromRes (f Nothing), rest)
+    short (OptArg f _ : _) xs rest = (fromRes (f (Just xs)), rest)
     short [] [] rest = (UnreqOpt optStr, rest)
     short [] xs rest = (UnreqOpt (optStr ++ xs), rest)
 
diff --git a/Cabal/src/Distribution/Simple/Command.hs b/Cabal/src/Distribution/Simple/Command.hs
index 937662b1d33..d3cff2db4e8 100644
--- a/Cabal/src/Distribution/Simple/Command.hs
+++ b/Cabal/src/Distribution/Simple/Command.hs
@@ -73,7 +73,6 @@ module Distribution.Simple.Command
   , reqArg'
   , optArg
   , optArg'
-  , optArgDef'
   , noArg
   , boolOpt
   , boolOpt'
@@ -139,7 +138,7 @@ data OptDescr a
       OptFlags
       ArgPlaceHolder
       (ReadE (a -> a))
-      (String, a -> a)
+      (a -> a)
       (a -> [Maybe String])
   | ChoiceOpt [(Description, OptFlags, a -> a, a -> Bool)]
   | BoolOpt
@@ -152,7 +151,7 @@ data OptDescr a
 fmapOptDescr :: forall a b. (b -> a) -> (a -> (b -> b)) -> OptDescr a -> OptDescr b
 fmapOptDescr x u = \case
   ReqArg d o p upd get -> ReqArg d o p (fmap m upd) (get . x)
-  OptArg d o p upd (str, g) get -> OptArg d o p (fmap m upd) (str, m g) (get . x)
+  OptArg d o p upd g get -> OptArg d o p (fmap m upd) (m g) (get . x)
   ChoiceOpt opts -> ChoiceOpt $ fmap (\(d, o, upd, get) -> (d, o, m upd, get . x)) opts
   BoolOpt d true false upd get -> BoolOpt d true false (\b -> m $ upd b) (get . x)
   where
@@ -242,16 +241,16 @@ optArg
   :: Monoid b
   => ArgPlaceHolder
   -> ReadE b
-  -> (String, b)
+  -> b
   -> (b -> [Maybe String])
   -> MkOptDescr (a -> b) (b -> a -> a) a
-optArg ad mkflag (dv, mkDef) showflag sf lf d get set =
+optArg ad mkflag mkDef showflag sf lf d get set =
   OptArg
     d
     (sf, lf)
     ad
     (fmap (\a b -> set (get b <> a) b) mkflag)
-    (dv, \b -> set (get b <> mkDef) b)
+    (\b -> set (get b <> mkDef) b)
     (showflag . get)
 
 -- | (String -> a) variant of "reqArg"
@@ -272,16 +271,7 @@ optArg'
   -> (b -> [Maybe String])
   -> MkOptDescr (a -> b) (b -> a -> a) a
 optArg' ad mkflag showflag =
-  optArg ad (succeedReadE (mkflag . Just)) ("", mkflag Nothing) showflag
-
-optArgDef'
-  :: Monoid b
-  => ArgPlaceHolder
-  -> (String, Maybe String -> b)
-  -> (b -> [Maybe String])
-  -> MkOptDescr (a -> b) (b -> a -> a) a
-optArgDef' ad (dv, mkflag) showflag =
-  optArg ad (succeedReadE (mkflag . Just)) (dv, mkflag Nothing) showflag
+  optArg ad (succeedReadE (mkflag . Just)) (mkflag Nothing) showflag
 
 noArg :: Eq b => b -> MkOptDescr (a -> b) (b -> a -> a) a
 noArg flag sf lf d = choiceOpt [(flag, (sf, lf), d)] sf lf d
@@ -357,8 +347,8 @@ viewAsGetOpt (OptionField _n aa) = concatMap optDescrToGetOpt aa
   where
     optDescrToGetOpt (ReqArg d (cs, ss) arg_desc set _) =
       [GetOpt.Option cs ss (GetOpt.ReqArg (runReadE set) arg_desc) d]
-    optDescrToGetOpt (OptArg d (cs, ss) arg_desc set (dv, def) _) =
-      [GetOpt.Option cs ss (GetOpt.OptArg dv set' arg_desc) d]
+    optDescrToGetOpt (OptArg d (cs, ss) arg_desc set def _) =
+      [GetOpt.Option cs ss (GetOpt.OptArg set' arg_desc) d]
       where
         set' Nothing = Right def
         set' (Just txt) = runReadE set txt
@@ -392,13 +382,13 @@ liftOptDescr get' set' (ChoiceOpt opts) =
     [ (d, ff, liftSet get' set' set, get . get')
     | (d, ff, set, get) <- opts
     ]
-liftOptDescr get' set' (OptArg d ff ad set (dv, mkDef) get) =
+liftOptDescr get' set' (OptArg d ff ad set mkDef get) =
   OptArg
     d
     ff
     ad
     (liftSet get' set' `fmap` set)
-    (dv, liftSet get' set' mkDef)
+    (liftSet get' set' mkDef)
     (get . get')
 liftOptDescr get' set' (ReqArg d ff ad set get) =
   ReqArg d ff ad (liftSet get' set' `fmap` set) (get . get')
diff --git a/Cabal/src/Distribution/Simple/Setup/Common.hs b/Cabal/src/Distribution/Simple/Setup/Common.hs
index 83ed76a16ed..eafc89f47fc 100644
--- a/Cabal/src/Distribution/Simple/Setup/Common.hs
+++ b/Cabal/src/Distribution/Simple/Setup/Common.hs
@@ -400,7 +400,7 @@ optionVerbosity get set =
     ( optArg
         "n"
         (fmap Flag flagToVerbosity)
-        (show verbose, Flag verbose) -- default Value if no n is given
+        (Flag verbose)
         (fmap (Just . showForCabal) . flagToList)
     )
 
@@ -418,7 +418,7 @@ optionNumJobs get set =
     ( optArg
         "NUM"
         (fmap Flag numJobsParser)
-        ("$ncpus", Flag Nothing)
+        (Flag Nothing)
         (map (Just . maybe "$ncpus" show) . flagToList)
     )
   where
diff --git a/Cabal/src/Distribution/Simple/Setup/Config.hs b/Cabal/src/Distribution/Simple/Setup/Config.hs
index 839241eed0f..7e26a085b73 100644
--- a/Cabal/src/Distribution/Simple/Setup/Config.hs
+++ b/Cabal/src/Distribution/Simple/Setup/Config.hs
@@ -567,9 +567,9 @@ configureOptions showOrParseArgs =
           "optimization"
           configOptimization
           (\v flags -> flags{configOptimization = v})
-          [ optArgDef'
+          [ optArg'
               "n"
-              (show NoOptimisation, Flag . flagToOptimisationLevel)
+              (Flag . flagToOptimisationLevel)
               ( \case
                   Flag NoOptimisation -> []
                   Flag NormalOptimisation -> [Nothing]
diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index 54279f74ef9..e0d65c78fdb 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -201,7 +201,7 @@ outdatedOptions _showOrParseArgs =
       ( optArg
           "PKGS"
           ignoreMajorVersionBumpsParser
-          ("", Just IgnoreMajorVersionBumpsAll)
+          (Just IgnoreMajorVersionBumpsAll)
           ignoreMajorVersionBumpsPrinter
       )
   ]
diff --git a/cabal-install/src/Distribution/Client/Setup.hs b/cabal-install/src/Distribution/Client/Setup.hs
index 3acbd6b8f0c..1e2282a2d0e 100644
--- a/cabal-install/src/Distribution/Client/Setup.hs
+++ b/cabal-install/src/Distribution/Client/Setup.hs
@@ -1017,7 +1017,7 @@ configureExOptions _showOrParseArgs src =
       ( optArg
           "DEPS"
           (parsecToReadEErr unexpectMsgString relaxDepsParser)
-          (show RelaxDepsAll, Just RelaxDepsAll)
+          (Just RelaxDepsAll)
           relaxDepsPrinter
       )
   , option
@@ -1029,7 +1029,7 @@ configureExOptions _showOrParseArgs src =
       ( optArg
           "DEPS"
           (parsecToReadEErr unexpectMsgString relaxDepsParser)
-          (show RelaxDepsAll, Just RelaxDepsAll)
+          (Just RelaxDepsAll)
           relaxDepsPrinter
       )
   , option
@@ -1948,7 +1948,7 @@ getCommand =
                     (const "invalid source-repository")
                     (fmap (toFlag . Just) parsec)
                 )
-                ("", Flag Nothing)
+                (Flag Nothing)
                 (map (fmap show) . flagToList)
             )
         , option
@@ -2832,7 +2832,7 @@ optionNumJobs get set =
     ( optArg
         "NUM"
         (fmap Flag numJobsParser)
-        ("", Flag Nothing)
+        (Flag Nothing)
         (map (Just . maybe "$ncpus" show) . flagToList)
     )
   where