diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,8 @@
+# 2.1.1
+
+* Relax version bounds
+* Remove dependency on `mtl`
+
 # 2.1.0
 
 * Relax upper version bounds for `aeson` to `(>= 1.3 && < 1.6)`
diff --git a/servant-jsonrpc-server.cabal b/servant-jsonrpc-server.cabal
--- a/servant-jsonrpc-server.cabal
+++ b/servant-jsonrpc-server.cabal
@@ -1,7 +1,7 @@
 cabal-version:       2.4
 
 name:                servant-jsonrpc-server
-version:             2.1.0
+version:             2.1.1
 author:              Ian Shipman <ics@gambolingpangolin.com>
 maintainer:          Ian Shipman <ics@gambolingpangolin.com>
 
@@ -30,10 +30,9 @@
     Servant.Server.JsonRpc
 
   build-depends:
-      aeson                 >= 1.3          && < 1.6
+      aeson                 >= 1.3          && < 2.1
     , base                  >= 4.11         && < 5.0
     , containers            >= 0.5          && < 0.7
-    , mtl                   >= 2.2          && < 2.3
-    , servant               >= 0.14         && < 0.19
+    , servant               >= 0.14         && < 0.20
     , servant-jsonrpc       >= 1.0.1        && < 1.2
-    , servant-server        >= 0.14         && < 0.19
+    , servant-server        >= 0.14         && < 0.20
diff --git a/src/Servant/Server/JsonRpc.hs b/src/Servant/Server/JsonRpc.hs
--- a/src/Servant/Server/JsonRpc.hs
+++ b/src/Servant/Server/JsonRpc.hs
@@ -47,12 +47,15 @@
 import qualified Data.Map.Strict          as Map
 import           Data.Proxy               (Proxy (..))
 import           GHC.TypeLits             (KnownSymbol, symbolVal)
-import           Servant.API              ((:<|>) (..), (:>), JSON,
-                                           NoContent (..), Post, ReqBody)
+import           Servant.API              (NoContent (..), Post, ReqBody,
+                                           (:<|>) (..), (:>))
 import           Servant.API.ContentTypes (AllCTRender (..))
 
 #if MIN_VERSION_servant_server(0,18,0)
-import           Servant.Server           (Handler, HasServer (..), HasContextEntry, type (.++), DefaultErrorFormatters, ErrorFormatters)
+import           Servant.Server           (DefaultErrorFormatters,
+                                           ErrorFormatters, Handler,
+                                           HasContextEntry, HasServer (..),
+                                           type (.++))
 #elif MIN_VERSION_servant_server(0,14,0)
 import           Servant.Server           (Handler, HasServer (..))
 #endif
@@ -65,7 +68,7 @@
 data PossibleContent a = SomeContent a | EmptyContent
 
 
-instance ToJSON a => AllCTRender '[JSON] (PossibleContent a) where
+instance ToJSON a => AllCTRender '[JSONRPC] (PossibleContent a) where
     handleAcceptH px h = \case
         SomeContent x -> handleAcceptH px h x
         EmptyContent  -> handleAcceptH px h NoContent
@@ -75,8 +78,8 @@
 
 
 type RawJsonRpcEndpoint
-    = ReqBody '[JSON] (Request Value)
-   :> Post '[JSON] PossibleJsonRpcResponse
+    = ReqBody '[JSONRPC] (Request Value)
+   :> Post '[JSONRPC] PossibleJsonRpcResponse
 
 
 #if MIN_VERSION_servant_server(0,18,0)