diff --git a/lisa.cabal b/lisa.cabal
index c9e7a25..942e96b 100644
--- a/lisa.cabal
+++ b/lisa.cabal
@@ -31,6 +31,7 @@ library
       Paths_lisa
   hs-source-dirs:
       src
+  ghc-options: -W
   build-depends:
       Spock >=0.14
     , aeson >=2.0
diff --git a/package.yaml b/package.yaml
index 3aa6e6b..24adb01 100644
--- a/package.yaml
+++ b/package.yaml
@@ -29,6 +29,8 @@ dependencies:
 
 library:
   source-dirs: src
+  ghc-options:
+  - -W
 
 executables:
   lisa-exe:
diff --git a/src/Lisa/Squeak.hs b/src/Lisa/Squeak.hs
index 069d203..9230f4e 100644
--- a/src/Lisa/Squeak.hs
+++ b/src/Lisa/Squeak.hs
@@ -7,11 +7,11 @@ module Lisa.Squeak where
 
 import Control.Applicative ((<|>))
 import Control.Monad.IO.Class (MonadIO, liftIO)
-import Data.Aeson (FromJSON(parseJSON), FromJSONKey(fromJSONKey), Options(fieldLabelModifier), ToJSON(toJSON), Value, (.:), (.:?), (.=), defaultOptions, genericParseJSON, genericToJSON, object, withObject)
+import Data.Aeson (FromJSON(parseJSON), Options(fieldLabelModifier), ToJSON(toJSON), (.:), (.=), defaultOptions, genericParseJSON, genericToJSON, object, withObject)
 import Data.Text (Text)
 import Data.Time.Calendar (Day)
 import GHC.Generics (Generic)
-import Network.HTTP.Req (Option, Scheme(..), POST(..), ReqBodyJson(..), Req, Scheme, Url, defaultHttpConfig, http, https, port, jsonResponse, responseBody, req, runReq)
+import Network.HTTP.Req (Option, Scheme(..), POST(..), ReqBodyJson(..), Url, defaultHttpConfig, http, port, jsonResponse, responseBody, req, runReq)
 
 import qualified Data.Char as Char
 
@@ -105,9 +105,11 @@ removePrefixModifier prefix = lowercaseFirst . stripPrefix prefix
         stripPrefix [] word = word
         stripPrefix (p:ps) (c:cs)
             | p == c    = stripPrefix ps cs
-            | otherwise = error $ "Invalid prefix " ++ ps ++ " (" ++ prefix ++ ") for key " ++ cs
+            | otherwise = error $ "Invalid prefix " ++ (p:ps) ++ " (" ++ prefix ++ ") for key " ++ (c:cs)
         stripPrefix _ [] = error $ "Prefix " ++ prefix ++ " is too long"
+
         lowercaseFirst (c:cs) = Char.toLower c : cs
+        lowercaseFirst [] = error $ "Prefix " ++ prefix ++ " ate all my input"
 
 removePrefixOpts prefix = defaultOptions { fieldLabelModifier = removePrefixModifier prefix }