diff --git a/changelog.d/1432 b/changelog.d/1432
new file mode 100644
index 00000000..f88207b9
--- /dev/null
+++ b/changelog.d/1432
@@ -0,0 +1,9 @@
+synopsis: Fixes encoding of URL parameters in servant-client
+prs: #1432
+issues: #1418
+description: {
+Some applications use query parameters to pass arbitrary (non-unicode) binary
+data.  This change modifies how servant-client handles query parameters, so
+that application developers can use `ToHttpApiData` to marshal binary data into
+query parameters.
+}
diff --git a/servant-client-core/src/Servant/Client/Core/HasClient.hs b/servant-client-core/src/Servant/Client/Core/HasClient.hs
index 5f7ad3b3..d598bf66 100644
--- a/servant-client-core/src/Servant/Client/Core/HasClient.hs
+++ b/servant-client-core/src/Servant/Client/Core/HasClient.hs
@@ -33,6 +33,9 @@ import           Control.Arrow
                  (left, (+++))
 import           Control.Monad
                  (unless)
+import qualified Data.ByteString as BS
+import           Data.ByteString.Builder
+                 (toLazyByteString)
 import qualified Data.ByteString.Lazy                     as BL
 import           Data.Either
                  (partitionEithers)
@@ -76,7 +79,7 @@ import           Servant.API
                  ReflectMethod (..), RemoteHost, ReqBody', SBoolI, Stream,
                  StreamBody', Summary, ToHttpApiData, ToSourceIO (..), Vault,
                  Verb, WithNamedContext, WithStatus (..), contentType, getHeadersHList,
-                 getResponse, toQueryParam, toUrlPiece)
+                 getResponse, toEncodedUrlPiece, toUrlPiece)
 import           Servant.API.ContentTypes
                  (contentTypes, AllMime (allMime), AllMimeUnrender (allMimeUnrender))
 import           Servant.API.TypeLevel (FragmentUnique, AtLeastOneFragment)
@@ -554,7 +557,7 @@ instance (KnownSymbol sym, ToHttpApiData a, HasClient m api, SBoolI (FoldRequire
       (Proxy :: Proxy mods) add (maybe req add) mparam
     where
       add :: a -> Request
-      add param = appendToQueryString pname (Just $ toQueryParam param) req
+      add param = appendToQueryString pname (Just $ encodeQueryParam param) req
 
       pname :: Text
       pname  = pack $ symbolVal (Proxy :: Proxy sym)
@@ -562,6 +565,9 @@ instance (KnownSymbol sym, ToHttpApiData a, HasClient m api, SBoolI (FoldRequire
   hoistClientMonad pm _ f cl = \arg ->
     hoistClientMonad pm (Proxy :: Proxy api) f (cl arg)
 
+encodeQueryParam :: ToHttpApiData a => a  -> BS.ByteString
+encodeQueryParam = BL.toStrict . toLazyByteString . toEncodedUrlPiece
+
 -- | If you use a 'QueryParams' in one of your endpoints in your API,
 -- the corresponding querying function will automatically take
 -- an additional argument, a list of values of the type specified
@@ -603,7 +609,7 @@ instance (KnownSymbol sym, ToHttpApiData a, HasClient m api)
                     )
 
     where pname = pack $ symbolVal (Proxy :: Proxy sym)
-          paramlist' = map (Just . toQueryParam) paramlist
+          paramlist' = map (Just . encodeQueryParam) paramlist
 
   hoistClientMonad pm _ f cl = \as ->
     hoistClientMonad pm (Proxy :: Proxy api) f (cl as)
diff --git a/servant-client-core/src/Servant/Client/Core/Request.hs b/servant-client-core/src/Servant/Client/Core/Request.hs
index 9196c795..bdc3e382 100644
--- a/servant-client-core/src/Servant/Client/Core/Request.hs
+++ b/servant-client-core/src/Servant/Client/Core/Request.hs
@@ -145,13 +145,13 @@ appendToPath :: Text -> Request -> Request
 appendToPath p req
   = req { requestPath = requestPath req <> "/" <> toEncodedUrlPiece p }
 
-appendToQueryString :: Text       -- ^ param name
-                    -> Maybe Text -- ^ param value
+appendToQueryString :: Text             -- ^ param name
+                    -> Maybe BS.ByteString -- ^ param value
                     -> Request
                     -> Request
 appendToQueryString pname pvalue req
   = req { requestQueryString = requestQueryString req
-                        Seq.|> (encodeUtf8 pname, encodeUtf8 <$> pvalue)}
+                        Seq.|> (encodeUtf8 pname, pvalue)}
 
 addHeader :: ToHttpApiData a => HeaderName -> a -> Request -> Request
 addHeader name val req
diff --git a/servant-client/src/Servant/Client/Internal/HttpClient.hs b/servant-client/src/Servant/Client/Internal/HttpClient.hs
index 61d51bc4..a2c6864d 100644
--- a/servant-client/src/Servant/Client/Internal/HttpClient.hs
+++ b/servant-client/src/Servant/Client/Internal/HttpClient.hs
@@ -46,7 +46,7 @@ import qualified Data.ByteString.Lazy        as BSL
 import           Data.Either
                  (either)
 import           Data.Foldable
-                 (toList)
+                 (foldl',toList)
 import           Data.Functor.Alt
                  (Alt (..))
 import           Data.Maybe
@@ -63,7 +63,7 @@ import           GHC.Generics
 import           Network.HTTP.Media
                  (renderHeader)
 import           Network.HTTP.Types
-                 (hContentType, renderQuery, statusCode, Status)
+                 (hContentType, renderQuery, statusCode, urlEncode, Status)
 import           Servant.Client.Core
 
 import qualified Network.HTTP.Client         as Client
@@ -238,7 +238,7 @@ defaultMakeClientRequest burl r = Client.defaultRequest
     , Client.path = BSL.toStrict
                   $ fromString (baseUrlPath burl)
                  <> toLazyByteString (requestPath r)
-    , Client.queryString = renderQuery True . toList $ requestQueryString r
+    , Client.queryString = buildQueryString . toList $ requestQueryString r
     , Client.requestHeaders =
       maybeToList acceptHdr ++ maybeToList contentTypeHdr ++ headers
     , Client.requestBody = body
@@ -289,6 +289,13 @@ defaultMakeClientRequest burl r = Client.defaultRequest
         Http -> False
         Https -> True
 
+    -- Query string builder which does not do any encoding
+    buildQueryString = ("?" <>) . foldl' addQueryParam mempty
+
+    addQueryParam qs (k, v) =
+          qs <> (if BS.null qs then mempty else "&") <> urlEncode True k <> foldMap ("=" <>) v
+
+
 catchConnectionError :: IO a -> IO (Either ClientError a)
 catchConnectionError action =
   catch (Right <$> action) $ \e ->
diff --git a/servant-client/test/Servant/ClientTestUtils.hs b/servant-client/test/Servant/ClientTestUtils.hs
index 842712e1..198c6462 100644
--- a/servant-client/test/Servant/ClientTestUtils.hs
+++ b/servant-client/test/Servant/ClientTestUtils.hs
@@ -24,9 +24,15 @@ import           Prelude.Compat
 
 import           Control.Concurrent
                  (ThreadId, forkIO, killThread)
+import           Control.Monad
+                 (join)
 import           Control.Monad.Error.Class
                  (throwError)
 import           Data.Aeson
+import           Data.ByteString
+                 (ByteString)
+import           Data.ByteString.Builder
+                 (byteString)
 import qualified Data.ByteString.Lazy             as LazyByteString
 import           Data.Char
                  (chr, isPrint)
@@ -54,10 +60,10 @@ import           Web.FormUrlEncoded
 import           Servant.API
                  ((:<|>) ((:<|>)), (:>), AuthProtect, BasicAuth,
                  BasicAuthData (..), Capture, CaptureAll, DeleteNoContent,
-                 EmptyAPI, FormUrlEncoded, Fragment, Get, Header, Headers,
+                 EmptyAPI, FormUrlEncoded, Fragment, FromHttpApiData (..), Get, Header, Headers,
                  JSON, MimeRender (mimeRender), MimeUnrender (mimeUnrender),
                  NoContent (NoContent), PlainText, Post, QueryFlag, QueryParam,
-                 QueryParams, Raw, ReqBody, StdMethod (GET), UVerb, Union,
+                 QueryParams, Raw, ReqBody, StdMethod (GET), ToHttpApiData (..), UVerb, Union,
                  WithStatus (WithStatus), addHeader)
 import           Servant.Client
 import qualified Servant.Client.Core.Auth         as Auth
@@ -109,6 +115,10 @@ type Api =
   :<|> "captureAll" :> CaptureAll "names" String :> Get '[JSON] [Person]
   :<|> "body" :> ReqBody '[FormUrlEncoded,JSON] Person :> Post '[JSON] Person
   :<|> "param" :> QueryParam "name" String :> Get '[FormUrlEncoded,JSON] Person
+  -- This endpoint makes use of a 'Raw' server because it is not currently
+  -- possible to handle arbitrary binary query param values with
+  -- @servant-server@
+  :<|> "param-binary" :> QueryParam "payload" UrlEncodedByteString :> Raw
   :<|> "params" :> QueryParams "names" String :> Get '[JSON] [Person]
   :<|> "flag" :> QueryFlag "flag" :> Get '[JSON] Bool
   :<|> "fragment" :> Fragment String :> Get '[JSON] Person
@@ -143,6 +153,7 @@ getCapture      :: String -> ClientM Person
 getCaptureAll   :: [String] -> ClientM [Person]
 getBody         :: Person -> ClientM Person
 getQueryParam   :: Maybe String -> ClientM Person
+getQueryParamBinary :: Maybe UrlEncodedByteString -> HTTP.Method -> ClientM Response
 getQueryParams  :: [String] -> ClientM [Person]
 getQueryFlag    :: Bool -> ClientM Bool
 getFragment     :: ClientM Person
@@ -167,6 +178,7 @@ getRoot
   :<|> getCaptureAll
   :<|> getBody
   :<|> getQueryParam
+  :<|> getQueryParamBinary
   :<|> getQueryParams
   :<|> getQueryFlag
   :<|> getFragment
@@ -194,6 +206,13 @@ server = serve api (
                    Just "alice" -> return alice
                    Just n -> throwError $ ServerError 400 (n ++ " not found") "" []
                    Nothing -> throwError $ ServerError 400 "missing parameter" "" [])
+  :<|> const (Tagged $ \request respond ->
+          respond . maybe (Wai.responseLBS HTTP.notFound404 [] "Missing: payload")
+                          (Wai.responseLBS HTTP.ok200 [] . LazyByteString.fromStrict)
+                  . join
+                  . lookup "payload"
+                  $ Wai.queryString request
+       )
   :<|> (\ names -> return (zipWith Person names [0..]))
   :<|> return
   :<|> return alice
@@ -310,3 +329,12 @@ pathGen = fmap NonEmpty path
     filter (not . (`elem` ("?%[]/#;" :: String))) $
     filter isPrint $
     map chr [0..127]
+
+newtype UrlEncodedByteString = UrlEncodedByteString { unUrlEncodedByteString :: ByteString }
+
+instance ToHttpApiData UrlEncodedByteString where
+    toEncodedUrlPiece = byteString . HTTP.urlEncode True . unUrlEncodedByteString
+    toUrlPiece = decodeUtf8 . HTTP.urlEncode True . unUrlEncodedByteString
+
+instance FromHttpApiData UrlEncodedByteString where
+    parseUrlPiece = pure . UrlEncodedByteString . HTTP.urlDecode True . encodeUtf8
diff --git a/servant-client/test/Servant/SuccessSpec.hs b/servant-client/test/Servant/SuccessSpec.hs
index 8729caf0..6b9f3bd0 100644
--- a/servant-client/test/Servant/SuccessSpec.hs
+++ b/servant-client/test/Servant/SuccessSpec.hs
@@ -22,11 +22,13 @@ import           Prelude ()
 import           Prelude.Compat
 
 import           Control.Arrow
-                 (left)
+                 ((+++), left)
 import           Control.Concurrent.STM
                  (atomically)
 import           Control.Concurrent.STM.TVar
                  (newTVar, readTVar)
+import qualified Data.ByteString as BS
+import qualified Data.ByteString.Lazy as BL
 import           Data.Foldable
                  (forM_, toList)
 import           Data.Maybe
@@ -93,6 +95,11 @@ successSpec = beforeAll (startWaiApp server) $ afterAll endWaiApp $ do
       Left (FailureResponse _ r) <- runClient (getQueryParam (Just "bob")) baseUrl
       responseStatusCode r `shouldBe` HTTP.Status 400 "bob not found"
 
+    it "Servant.API.QueryParam binary data" $ \(_, baseUrl) -> do
+      let payload = BS.pack [0, 1, 2, 4, 8, 16, 32, 64, 128]
+          apiCall = getQueryParamBinary (Just $ UrlEncodedByteString payload) HTTP.methodGet
+      (show +++ responseBody) <$> runClient apiCall baseUrl `shouldReturn` Right (BL.fromStrict payload)
+
     it "Servant.API.QueryParam.QueryParams" $ \(_, baseUrl) -> do
       left show <$> runClient (getQueryParams []) baseUrl `shouldReturn` Right []
       left show <$> runClient (getQueryParams ["alice", "bob"]) baseUrl