diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## 1.0.3
+### Added
+- `readField` implementations for the custom `ParseField` instances to
+  accommodate a minor API change in `optparse-generic` version `1.2.3`
+
 ## 1.0.2
 ### Fixed
 
diff --git a/hocker.cabal b/hocker.cabal
--- a/hocker.cabal
+++ b/hocker.cabal
@@ -1,5 +1,5 @@
 name:                hocker
-version:             1.0.2
+version:             1.0.3
 synopsis:            Interact with the docker registry and generate nix build instructions
 homepage:            https://github.com/awakesecurity/hocker#readme
 Bug-Reports:         https://github.com/awakesecurity/hocker/issues
diff --git a/src/Hocker/Types.hs b/src/Hocker/Types.hs
--- a/src/Hocker/Types.hs
+++ b/src/Hocker/Types.hs
@@ -157,6 +157,7 @@
   deriving (Show)
 
 instance ParseField Credentials where
+  readField = Options.readerError "Internal, fatal error: unexpected use of readField"
   parseField _ _ _ = (Basic <$> parseUsername <*> parsePassword) <|> (BearerToken <$> parseToken)
     where
       parseUsername = Text.pack <$>
diff --git a/src/Hocker/Types/Hash.hs b/src/Hocker/Types/Hash.hs
--- a/src/Hocker/Types/Hash.hs
+++ b/src/Hocker/Types/Hash.hs
@@ -29,6 +29,7 @@
 readSHA256 = either (const Nothing) Hash.digestFromByteString . toBytes
 
 instance ParseField (Hash.Digest Hash.SHA256) where
+  readField = Options.maybeReader (readSHA256 . C8.pack)
   parseField h _ _ =
       (Options.option (Options.maybeReader (readSHA256 . C8.pack)) $
        ( Options.metavar "SHA256"
diff --git a/src/Hocker/Types/ImageName.hs b/src/Hocker/Types/ImageName.hs
--- a/src/Hocker/Types/ImageName.hs
+++ b/src/Hocker/Types/ImageName.hs
@@ -23,6 +23,7 @@
   deriving (Generic, Show)
 
 instance ParseField ImageName where
+  readField = ImageName <$> Options.str
   parseField _ _ _ =
     ImageName <$>
       (Options.argument Options.str $
diff --git a/src/Hocker/Types/ImageTag.hs b/src/Hocker/Types/ImageTag.hs
--- a/src/Hocker/Types/ImageTag.hs
+++ b/src/Hocker/Types/ImageTag.hs
@@ -23,6 +23,7 @@
   deriving (Generic, Show)
 
 instance ParseField ImageTag where
+  readField = ImageTag <$> Options.str
   parseField _ _ _ =
     ImageTag <$>
       (Options.argument Options.str $
diff --git a/src/Hocker/Types/URI.hs b/src/Hocker/Types/URI.hs
--- a/src/Hocker/Types/URI.hs
+++ b/src/Hocker/Types/URI.hs
@@ -31,6 +31,7 @@
       over _Left show parsedURI
 
 instance ParseField (URIRef Absolute) where
+  readField = uriReader
   parseField h n s =
       (Options.option uriReader $
        ( Options.metavar "URI"