diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+0.6.3
+
+* Add To/FromForm instances for () and Void
+
 0.6.2
 
 * Support GHC-9.12
diff --git a/http-api-data.cabal b/http-api-data.cabal
--- a/http-api-data.cabal
+++ b/http-api-data.cabal
@@ -1,6 +1,6 @@
 cabal-version:   1.12
 name:            http-api-data
-version:         0.6.2
+version:         0.6.3
 
 synopsis:        Converting to/from HTTP API data like URL pieces, headers and query parameters.
 category:        Web
@@ -47,7 +47,6 @@
                    , bytestring            >= 0.10.8.2 && < 0.13
                    , containers            >= 0.6.0.1  && < 0.8
                    , text                  >= 1.2.3.0  && < 1.3 || >=2.0 && <2.2
-                   , transformers          >= 0.5.6.2  && < 0.7
 
     -- other-dependencies
     build-depends:
@@ -94,8 +93,7 @@
                    , unordered-containers
                    , uuid-types
 
-    build-depends:   HUnit                >= 1.6.0.0  && <1.7
-                   , hspec                >= 2.7.1    && <2.12
+    build-depends:   hspec                >= 2.7.1    && <2.12
                    , QuickCheck           >= 2.13.1   && <2.16
                    , quickcheck-instances >= 0.3.25.2 && <0.4
 
diff --git a/src/Web/Internal/FormUrlEncoded.hs b/src/Web/Internal/FormUrlEncoded.hs
--- a/src/Web/Internal/FormUrlEncoded.hs
+++ b/src/Web/Internal/FormUrlEncoded.hs
@@ -49,7 +49,7 @@
                                              UTCTime, ZonedTime)
 import           Data.Time.Calendar.Month.Compat (Month)
 import           Data.Time.Calendar.Quarter.Compat (Quarter, QuarterOfYear (..))
-import           Data.Void                  (Void)
+import           Data.Void                  (Void, absurd)
 import           Data.Word                  (Word16, Word32, Word64, Word8)
 import           GHC.Exts                   (Constraint, IsList (..))
 import           GHC.Generics
@@ -267,6 +267,16 @@
 
 instance ToForm Form where toForm = id
 
+-- |
+--
+-- @since 0.6.3
+instance ToForm Void where toForm = absurd
+
+-- |
+--
+-- @since 0.6.3
+instance ToForm () where toForm _ = Form HashMap.empty
+
 instance (ToFormKey k, ToHttpApiData v) => ToForm [(k, v)] where
   toForm = fromList . map (toFormKey *** toQueryParam)
 
@@ -412,6 +422,16 @@
   fromForm = genericFromForm defaultFormOptions
 
 instance FromForm Form where fromForm = pure
+
+-- |
+--
+-- @since 0.6.3
+instance FromForm Void where fromForm _ = Left "fromForm: Void"
+
+-- |
+--
+-- @since 0.6.3
+instance FromForm () where fromForm _ = Right ()
 
 -- | _NOTE:_ this conversion is unstable and may result in different key order (but not values).
 instance (FromFormKey k, FromHttpApiData v) => FromForm [(k, v)] where
diff --git a/test/Web/Internal/FormUrlEncodedSpec.hs b/test/Web/Internal/FormUrlEncodedSpec.hs
--- a/test/Web/Internal/FormUrlEncodedSpec.hs
+++ b/test/Web/Internal/FormUrlEncodedSpec.hs
@@ -39,12 +39,12 @@
 
     it "is the right inverse of ToForm" $ property $ \x (y :: Int) -> do
       let f1 = fromList [("rec1", x), ("rec2", toQueryParam y)]
-          Right r1 = fromForm f1 :: Either Text SimpleRec
-      toForm r1 `shouldBe` f1
+          r1 = fromForm f1 :: Either Text SimpleRec
+      fmap toForm r1 `shouldBe` Right f1
 
     it "returns the underlying error" $ do
       let f = fromList [("rec1", "anything"), ("rec2", "bad")]
-          Left e = fromForm f :: Either Text SimpleRec
+          e = either id (const "no error") (fromForm f :: Either Text SimpleRec)
       unpack e `shouldContain` "input does not start with a digit"
 
 urlEncoding :: Spec